Why are relay pins numbered like that?

Steve answers the question ‘Why are relay terminals numbered 30, 85, 86, 87?’ He also has a funny way to remember them. Plus: a quick demonstration on how they work.
Amazon Affiliate link to the OTC relay pliers:
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#tooldemos

[@philscott7949]

6:26 Answer. You're welcome.

[@ToolDemos]

👍

[@kermets]

thats not the "Why" answer..... thats just how its wired

[@LegendLength]

Why start at 85 though?

[@wes3428]

Actually 1:16... but thanks for the red herring!

[@albatross5466]

It is German automotive wiring system. 15 is hot with ignition on, 30 is hot at all times, 31 is always grounded and the wires are brown.

[@ToolDemos]

Sometimes I wish there were one standard for all cars. That would solve a lot of problems.

[@Derpy1969]

It’s almost like he did not research whatsoever.

[@rickharriss]

WHY?

[@davidelliott5843]

So the 88 is nothing to do with Flak 88?

[@ToolDemos]

@@davidelliott5843 too soon?

[@nicholashacking381]

I've been on the planet for 60 years and I've been using relays for over 50 of those years. In all that time I didn't know where the numbers came from, until now. Thanks for enlightening me!

[@ToolDemos]

Very cool! Glad to help.

[@sgtbrown4273]

Good sir, I was in the same boat! I always thought it was a really cruel joke .

[@61rampy65]

On most, but not all, Bosch relays, 85 and 86 are interchangeable, meaning you can connect them in reverse order with no problems. Some of the older ones use a clamping diode instead of the resistor to control the flyback voltage, thus requiring wiring in the correct polarity.

[@ToolDemos]

Great information, thank you for that.

[@twowheeledparadox]

Freewheeling diode?

[@fourfortyroadrunner6701]

Not sure I agree on the "most" comment. Be careful, as using diode equipped relays, connected in reverse, can possibly damage solid state switching sources, the very thing they were meant to protect

[@MrTheHillfolk]

Sometimes the diagram printed on the relay will show the diode. Or of there's a part number you can Google it to try and find out if it has one or not.

[@TheSimoc]

There have always been and will always be relays with diode and relays with resistor, it has nothing to do with age. Actually, resistor, along with relay, is far older invention than diode.

[@Miata822]

Great video. I have taught this class many times. One little but important thing was left out though. Some relays have a diode rather than a resistor. The diode protects other devices on the circuit that may contain a microcontroller (computer). While a relay with a diode will work in any circuit it is critical to only replace a diode relay with another of the same type. Practical example- A relay had been replaced on the air conditioner of an off-road construction vehicle. The vehicle's engine began stalling intermittently. Diagnostics found no fault with the engine but an operator noticed that the engine stalled when he changed the air conditioner setting repeatedly. A resistor relay had been installed in place of a diode relay and the small voltage spike from the relay would sometimes cause the ECU to reset, stalling the engine.

[@ToolDemos]

Wow, that is a very strange problem. Glad they found it.

[@TurboTyTy]

Whoa that’s interesting & a very good find 👍🏽

[@daze1945]

I was going to mention the flywheel diode but you beat me to it. The resistor does allow for reverse polarity operating voltage. 👍

[@JITProductions]

The diode on the clutch solenoid is important too. The energy from a collapsing magnetic field has to go somewhere and it is better absorbed by a diode...As a general rule in my electronic circuit builds I always use a diode on the coil of a relay.

[@curtw8827]

A reverse diode on a DC relay coil gives a path for current caused by the collapsing magnetic field, reversing the DC voltage would be a dead short through the diode, so its not to make it bidirectional. I'm thinking the resistor across the coil is to allow the computer to monitor the integrity of the circuit when the coil is not commanded to be energized.

[@ehsnils]

All is explained in DIN 72552, and there's even a Wikipedia page for it.

[@ToolDemos]

Thanks

[@IscuAndrei]

People are gonna flame me for this correction: Voltage and Amperage are measurement units. Basically, you use Volts to measure Electrical Tension and Amperes measure Electrical current. Didn't mean to sound pedantic, just to share information, just like @Tool Demos did. Great info on the realy numbering! Enjoyed it.

[@ToolDemos]

Great point, I mix those terms when I shouldn't.

[@JamieBainbridge]

10 year old me, with Walkman parts all over the table, would be overjoyed to learn that 30 years in the future I can watch on-demand videos of people pulling things apart to learn how they work. Thanks for the education!

[@ToolDemos]

You and me both! I was the same as a kid.

[@chuckmaddison2924]

Keep going. If you look around you can find another use for DVD and Blueray burners . They make great lasers just be careful . The blu ray bit more of fiddley to work with.

[@claylong7074]

You have a brilliant approach to explaining why numbers like 87 are assigned to the pin numbers of relays using the DIN system, BUT, for dummies like me, you didn't actually explain why they didn't use "123" (as you mentioned) instead. I think you suggested they were just numbering circuits as they went along and when they got to relays, they had a number left to use like 87. I would like more light shed on that, like, what came before 87, and after, and the most important question. WHY?

[@ToolDemos]

Good point. Maybe there should be a follow up video.

[@alanreid3063]

mains relays /contactors use odd numbers for N.O. even for N.C. or vice versa can't remeber off hand, seems to me they are doing the same here. but the lower numbers are already used on other types of relays

[@JfromUK_]

You can find listings online of the terminal numbers in DIN 72552, which might help with that detail. 30 is just "battery positive" and so maybe came earlier because it relates to a lot of other things.

[@Oo-IIII-oO]

He did explain it: "german engineering"

[@justinwood2]

@@ToolDemos or maybe you should just rename the video to something that isn't misleading?

[@ajseusa1488]

Close to correct, but not quite. Yes, pin 85 is ground (-) and pin 86 is the positive (+) to the energizing coil to "turn on" and close the relay. But, pin 30 is usually used as the supply source (12v + or Ground -) and most circuits use pin 87 as the switched (NO Normally Open) item. Pin 87a is connected to pin 30 when the relay is off or (NC Normally Closed). [Note: Pin 87a (NC Normally Closed) may be missing on some relays]

[@ToolDemos]

You are correct

[@BuiltatBlackjacks]

If its supposed to be a negative terminal or ground, the terminal code is 31, 30 or 30a is always supposed to be battery positive, but in practice on a 4 pin relay you can usually swap 87 and 30 without an issue. 85 and 86 codes are used because relays can be switched on the high side or the low side so they aren't necessarily wired straight to ground.

[@BlackEpyon]

As a matter of fact, I wasn't wondering why those numbers.... BUT NOW THAT YOU BROUGHT IT UP...!

[@flagmichael]

WOW! After more than 50 years working with electronics, and DIYing my cars, I still only knew about the inscrutable and unexplained numbers on the relays. This is my eye=opener for the week... maybe month. Subscribing, of course.

[@ToolDemos]

Welcome and thanks.

[@nejic7809]

Electronics has never been my strong suit. I appreciate this vid!

[@oh2mp]

Every day you learn something new from the internet. I have played with those relays for decades and didn't know about the numbering. That Back To The Future memorizing hack was cool. In my native language, Finnish, there's one nice memorizing thing. Black is "musta" and red is "punainen". So the color names begin with the same letters as plus and minus. Easy to remember for beginners.

[@ToolDemos]

Thanks. That reminds me of a BMW wiring diagram, the colors were labeled with an abbreviation. I had no idea what SC was until I remembered that Schwartz means black.

[@abdul-kabiralegbe5660]

​@@ToolDemos Schwartz is a common name in German by the way. So the Germans also name people after colours, just like the English. Nice.

[@crazysquirrel9425]

Had a car that the horn relay went out. New one was a whopping $80! So I bought a fog light relay and wired it in. That relay was $10. Worked like a champ too. Probably better since it could handle more amperage than the OEM one.

[@ToolDemos]

Awesome! You’re not a victim of the ‘proprietary parts’ scam.

[@shaggydogg630]

Right way to do it!

[@1977jelliott]

Amperage... you mean current?

[@BareFootDuck]

​@@1977jelliott what's the difference?

[@1977jelliott]

@@BareFootDuck grammar

[@altvamp]

In the UK we call the diodes back or reverse emf protection diodes, also relays with this protection usually show the diode symbol on the relay along with the connection diagram.

[@blackrifle6736]

*Correct. Many folks have no clue about significance of that symbol. Thanks for pointing it out. Cheers!*

[@CZ350tuner]

Late 1960's onwards Skoda cars, Jawa & CZ motorcycles use the DIN automotive terminal coding. 30 = Battery live. 15 = Horn switch & flasher can power feed. 54 = ignition system power. 86 = Tail & parking lights. 87 = headlight switch power feed.

[@JBurris]

Is there a chart with this information or even more available somewhere? This is great, thank you.

[@garydobbins6622]

I owned a CZ 250 dirt bike that thing had unbelievable power but not competitive to the Jap bikes as it weighed a ton.

[@sgtbrown4273]

Well ill be a monkeys uncle. 45 year old master compressor technician here and I always wondered what sadist came up with that numbering system know I now. Should have known it was the Germans. Thank you good sir ! Subscribed.

[@ToolDemos]

Thanks and welcome.

[@billmoran3219]

The reason for a diode suppressor relay is to protect the circuit from the high voltage field that is present when a coil is shut down. It protects electronics from a voltage spike like a one way check valve.

[@teardowndan5364]

The resistor does the same job, albeit in a less efficient (wastes power while the relay is on) polarity-agnostic manner: if the coil draws 30mA, the 680ohm resistor will limit the back-EMF to 0.03x680 = 20.4V. One minor advantage from doing so is that the back-EMF energy gets dissipated quicker for slightly faster release than letting the current freewheel through a diode. Having a parallel resistor also makes it easy for the BCM/ECU/whatever to check whether the relay has a blown winding or external wiring issue. Whatever controls the relay likely has its own protection diodes as good practice anyway since failure of the relay's internal diode or resistor is always an option.

[@N4HHE]

When current flows through an inductor such as a relay coil the inductor likes to keep current flowing at constant rate. When one interrupts the current the magnetic field in the coil collapses (sourcing stored energy) to keep current flowing as long as it can, which can arc across switch contacts or damage semiconductor switches. As mentioned, this is how ignition coils spark spark plugs. The usual solution is to place a diode across the coil to loop the collapsing current back through the coil. Slight problem is this solution is polarity sensitive. A resistor is not, but not as good.

[@samueladitya1729]

@@teardowndan5364 but the resistor consume some fraction power of the relay, mean the relay will heat more during operation. why not just use back to back zener diode to limit the voltage?

[@teardowndan5364]

@@samueladitya1729 If you use straight zener diodes, there is nothing limiting current in case of an alternator voltage surge or a double-stacked jump-start. A parallel resistor won't mind seeing 28V for a few seconds while a 15-23V zener will most likely get instantaneously fried. Yet another issue is that diodes tend to fail shorted, which could destroy the BCM/ECU/whatever is controlling it while resistors practically always blow open. If you wanted to do bidirectional zener clamping on a relay, you'd need to throw in a resistor on top. That is becoming a lot of extra stuff to secure in there to save P = V^2/R = 13.5^2/680 = 0.27W of power in a machine that idles at ~5kW.

[@paulf1071]

If replacing a relay's internal damaged freewheeling diode, take care of polarity.

[@Heisrisin3]

No one complicate engineering and design like the Germans.

[@ToolDemos]

Truly.

[@briandurning9211]

Thanks for the Back to the Future tip. I appreciate the explanation and demo to bring the concept to reality.

[@ToolDemos]

You bet! I hope it helps.

[@rwcraver]

Regardless if they 'set' the standard, in Japanese car repair circles we refer to them as Botched, always over complicated. Control side and load side is all one needs to remember.

[@ToolDemos]

That’s pretty funny.

[@MustangFord]

Thank you!!! I can now understand how important these little relays are for automotive purposes. A thinner wire(s) can be threaded throughout the vehicle instead of thicker wire to basically do the exact same thing, like running a fuel pump. It's cheaper to use relays and saves weight. Amazing engineering.

[@ToolDemos]

You bet!

[@albanana683]

Moving a high amp circuit closer to the load is always an advantage. My 1960s Alfa was running all the headlamp current through the spindly switch on the steering column. When it fails, and it will, it's €€€€ to replace. Very little effort and relative cost, to relocate the power switching to relays next to the lights and battery.

[@tehgangstadawg]

You can also use a cheaper switch and the switch will last longer. DC switches arc more than AC switches and wear faster.

[@abdul-kabiralegbe5660]

The same concept of substitution works in maths: replacing something with something else that's functionally equivalent. Clever manipulation.👏🏻👏🏻

[@blackrifle6736]

@@albanana683 *Thank you for your "Alfa" explanation. Odds are good my long-gone Fiat Spyder used the same Magneti Marelli switch. Knowing Fiat's impecunious behaviours it was probably even same part number! Bought new, replaced one during two years of ownership. Good riddance to my first and last Fiat. Cheers!*

[@don2deliver]

some of the GM four pin relays can be fitted in either direction because 30 and 87 are on opposite corners as are 85 and 86. And they work with the coil poles either way.

[@ToolDemos]

I like that.

[@rbmwiv]

Haven’t watched the video yet but I’m pretty sure it’s a German wiring standard because that’s all I have worked on since 1992 so I see those pins in my sleep. I remember in high school my sisters BMW wouldn’t start sometimes it was a interment problem that I found was a short on the trigger wire. It was the fuel pump relay so I made a jumper wire and used a paint marker to mark the 2 terminals she needed to plug into. It got her by for a few months until I was able to get a service manual for the car and then I was able to use the schematic to diagnose it. Great video though.

[@ToolDemos]

Had that same problem with an old Bimmer.

[@rbmwiv]

@@ToolDemos was it a e21 320i? Because BMWS was the first German cars I started working on and I know all the quarks of them and all the known issues, and that turned out to be a very common failure on that model.

[@ToolDemos]

@@rbmwiv yup, an old beater we had in the late 90’s living in Germany.

[@joebledsoe257]

I had some equipment that used a Form Z relay as an ac motor reverser. Interesting. Saw my work buds burn up a number of items because they were accustomed to typical Form A, B, and C relays. I found a chart that had a listing of "every relay" form type and each one's variables, IE: Diodes Resistors, Capacitors, ETC., and got a Happy Award (but no extra money) for fixing an internal company problem. It taught me to not memorize any relay or other connection numbering, as another equipment manufacturer may do something different, so I always reference the MFG's wiring diagrams and caught a few errors there too. I never burnt anything with a wiring error. I say "every relay" with trepidation as stuff is always changing and new things come along.

[@ToolDemos]

Sounds like you are the go-to guy when things get serious.

[@static-san]

The numbers describe the purpose of the connection; they're not really pin numbers. So you'll see the numbers at 6:40 on other things, too, such as the ignition switch. You can see this if you look at a modern current-flow circuit for a car. The Porsche 924 I used to own was like that: at the top of the circuit diagram were several numbered "buss" lines and they were numbered 30, 85, 86, etc. according to their purpose.

[@abdul-kabiralegbe5660]

Yeah. What beats me are those with the alphabet suffixes like 30N, 15F (examples of the format). I can recognise the numbers but have no definite clue as to the suffix.

[@stangei000]

This was the first Video i´fe seen from you and i like your way to explain these things to people who maybe don´t have the knowlege about it like a car mecanic. By the way, your pronouncing on Deutsches Instiut für Normung was awesome for a non nativ speaker. For those who interested in some Backgroundinformations from a german Car-electrition: 30 is always called every cable that comes directly from battery positiv without a switch in it. As soon as you put a switch on it, the number changes depending, what it should powers. for example: parklight is number 58, ignition switch for maybe the radio or enginecontroler is number 15 and Brakelight is number 54. some of these can be switched from a Relais but because the relais can fit in any socket they needed for, they needed an universal number for the output, and that´s the 87.

[@ToolDemos]

dankeschön. Also, thank you for your experienced insight.

[@curthenry9398]

Thank you for the video. I have always used a meter to find the coil circuit of a relay, hopefully I will remember the numbering system.

[@ToolDemos]

I hope it helps.

[@PhG1961]

Interesting video! Also worth mentioning is that some of these relays have an internal diode mounted parallel on the contacts of the coil. A so called freewheeling or flyback diode. This is to reduce inductive voltages when the relay is turned off and so preventing to do damage to sensitive components in the system. High quality automotive relays also come with sheelding on the inside, to block off RF signals produced by the coil when switching. Also the closing/opening from the contacts cause 'spikes' in the RF spectrum which can cause interference. At the same time, the inside is protected from RF signals coming into the relay. Years ago I had quite some issues with VHF radiotranceivers that interferred with relays. For instance, when the PTT button was pressed and the direction indicator was on, the blinking speed of the indicator doubled. Another one... airbags popping out when the radio was operated. Therefore, we always did a small test. We took the car for a spin at a low speed and crossed our fingers. Fortunately, I never had an airbag going off, but I know some cases...

[@ToolDemos]

Oh wow

[@rty1955]

Actually its is called BACK EMF And also a diode is MUCH quicker to dissipate the back EMF v. A simple resistor. When a voltage is applied to a coil, magnetic energy is produced in the coil, this attracting the metal bar which makes the electrical connection. But when voltage is removed, the magnetic energy collapses back ito the coil, which cause the coil to GENERATE a voltage. Sometime MUCH higher than the input voltage. This back EMF needs to be clamped. This is what the diode does. The diode is oriented in the opposite direction of the normal current flow to the relay therefore no current will flow thru the diode when the coil is energized but when the power is removed, the back EMF will flow thru the diode back to the other side of the coil. In effect shorting out the voltage (back EMF) diodes are MUCH quicker than a resistor and thats why they are used. A driver circuit such as on a car computer can be destroyed in a few microseconds, so its best to protect the driving circuit. Sometimes people may place a clamping circuit on the driving printed circuit, but its best to clamp it at the source.

[@abdul-kabiralegbe5660]

​@@rty1955 Thanks for the clear info!

[@scottwillis5434]

@@rty1955 Back EMF, yes. However the higher the voltage across the circuit during the inductive spike, the faster the energy dissipates; a simple diode gives about a 1V drop, a resistor a voltage proportional to the (remaining) current, and a Zener diode (plus a simple diode to prevent forward conduction in the Zener) the relatively constant Zener voltage.

[@auldteuchter9012]

@@rty1955 I hope you are not offended but you're not quite right about diode versus resistor. The faster the field collapses the faster the relay will open -- at the expense of higher spike voltage. A resistor absorbs energy but a diode facilitates circulating current and lengthens opening time. Quick calculation using ball-park figures and 680 ohms, the coil current falling to half value is about 4 times as long with a diode as it is with the resistor.

[@JayFude]

The old, big round computer keyboard connector was known as a 5-pin DIN. Another DIN that is quite common is for Microphones, like what pros use. MIDI also uses a similar DIN plug. Those damn Germans, just like the English language, they are everywhere.

[@ToolDemos]

Americans have KFC, Germans have DIN.

[@137bob3d]

oct 14 , 2023 Colorado , USA well done . the size difference of the metal tabs was an informative clue for telling coil ma drivers or output hi-amps switch. and how the hi-A switch can have 3 tabs not just 2. depending on if the default is 'on' and the relay is to turn it off. or vice-versa my one Carrrier house furnace circuit board fails the self-test due to a relay for the blower motor not working. now my confidence is raised for getting in there and fixing or replacing it with a new one

[@ToolDemos]

That’s great! Hope it goes well for ya.

[@jmer3536]

I learned so much more about how a relay works. Thanks!

[@ToolDemos]

Glad it helped!

[@ronwade5646]

B plus or, B+ is an old military radio reference, in WWI Military radio Gear, and by WWII A TON of military radios used two batteries to power the tube type equipment. Battery A was usually 6-12 volts and lit the filaments, the B battery was quite a high voltage and drove the plate circuits. Today many automotive wiring diagrams still call the battery, B+.

[@ToolDemos]

That’s really neat.

[@tedwalford7615]

Wow. I was today years old when I incidentally learned from this video the trick of using Vise Grips pliers for establishing connections to car battery terminals. Yikes. Well, thank you for that too!

[@ToolDemos]

That’s pretty cool, bonus skill!

[@redmesa2975]

When I was a transit bus tech for 15 years, we only needed to know the basics. 85-86 is the coil terminals. 30 is the common terminal ( power) 87a normally closed. 87 normally open. We where taught some relays had a diode. But I don’t remember the reason. You and some of the commentators,did a great job explaining. Our older coaches used relay logic on many circuits. The newer coaches after 2004 or so where multiplexed.

[@ToolDemos]

I miss old stuff sometimes.

[@picklerix6162]

The diode is supposed to protect transistors from the inductive voltage kick when the coil power is removed. The voltage from the inductive kick can destroy unprotected semiconductors. You often see these protection diodes in MOSFETs since they can be destroyed by high voltages.

[@redmesa2975]

@@picklerix6162 I was taught in bus multi plex class, that the modules use MOSFET transistors. Because they can handle up to 10 amps of output current. Didn’t realize a voltage spike would damage them.

[@chrisquinlan3012]

I found a list of terminal numbers with written explanation in a old catalogue years ago .Titled ,"Terminal designations in accordance with DIN 72 552 " .Its 2 A4 PAGES wIth over 100 terminal numbers and terminal definition.Absolute GOLD .

[@ToolDemos]

Right on.

[@Fine_i_set_the_handle]

Really wish they would have borrowed from industrial standards and used a1 and a2 for the coil at least.

[@blackrifle6736]

*You're overlooking fact this electrical standard numbering system originated in Germany, not USA. DIN predated ASA (American Standard Association) by decades. Essentially, Germans got their act together first therefore DIN was adopted world-wide first. USA was and is such a huge market that DIN-compliance was non-significant here. WW1 and WW2 might also had some influence on decision-makers. Cheers!*

[@Fine_i_set_the_handle]

@@blackrifle6736 The relay was invented after both standards stood. It's literally as simple as bosch is a German company so they used German standards. Nothing to do with what was standardized first.

[@blackrifle6736]

@@Fine_i_set_the_handle *Very well. Makes sense to me. Cheers!*

[@rhyoliteaquacade]

Thanks! I have always wondered even back to my first VW beetle, why they numbered relays like that.

[@ToolDemos]

Glad to help answer that.

[@WireWeHere]

Relay important information to switch your thinking. Waited a long time for that one to work.

[@ToolDemos]

Perfect!

[@anthonywilson4873]

The resistor across the coil contacts absorbs electrical spikes, this type of protection is very common in the US and is not polarity sensitive . Bosch relays very often use diodes to do the same thing these are electrical one way valves which again allow the spike to be absorbed, these are polarity sensitive, hook the coil up the wrong way and there will be a bang as the diode explodes. Both resistors or diode protect sensitive electronic controllers from reverse electro motives forces (Back EMF) spikes. When coils are switched off the established generated magnetic field collapsing produces a high voltage spike flowing in the opposite direction to that used to operate the coil, as mention just like an ignition coil on a petrol engine. These reverse EMF Spikes can destroy an ECU control circuit maybe not straight away but grab an IGN wire and see how you feel😀. Some simple relays do not have these and are cheaper to buy and far more expensive if installed in place of a spike protected relay. How much is an ECU??

[@ToolDemos]

Very well said.

[@al_dente4777]

Wow. I always wondered what those resistors were for. I used a couple of those resistorless decades-old relays for a supplemental horn set-up, without knowing that I should beware of using these on vehicles equipped with board computers. Lucky for me, the horn circuit is entirely separate from any computer

[@ToolDemos]

Good thing.

[@abdul-kabiralegbe5660]

Yeah, I suppose the horn circuit in your vehicle is that way. Some others have a microcontroller handling the usually integrated relay. I think the mid to late 2000s Lexus IS350 is that way.

[@zippie2787]

horn circuits are actually not separate from a computer, Body Control Modules (BCMs) regularly control horn relays in tandem with the horn switch on the steering wheel, because when you lock your car your horn blasts to let you know you locked it, that's the BCM completing the horn relay's coil circuit to ground.

[@kensakamoto258]

THANK YOU!! I have been doing mobile electronics for years and didn't know that!

[@ToolDemos]

That’s cool, I love learning new things too.

[@frankiec8955]

Great explanation on how the relay is set up and works!

[@ToolDemos]

Thanks

[@62Cristoforo]

I can’t believe this kind of information isn’t more widely known among mechanics when it comes to those cryptic numbers stamped on relays. I mean, they seem pretty definite, and everyone who works on cars seems to know what they mean, or at least accepts them as normal. Thanks.

[@micualex9799]

Why would mecanics bother with understanding of electricity? Let the electricians do their stuff!

[@abdul-kabiralegbe5660]

That which shall not be mentioned. 😂👻

[@blackrifle6736]

@@micualex9799 *Because over the last 100 years, "mechanics" as you call them have also been electrical technicians. They have also been electronics techs for only the last 40 or so. To better understand, try walking in their shoes for awhile.*

[@micualex9799]

@@blackrifle6736 To understand is one thing, to apply what you understood is another. What I'm trying to say here is not to offend or create a discussion out of it. Simply I want to highlight that if you don't understand by all means how electricity works you should stay away and let professionals to carry that job. I've seen many cases when mecanic s tried "their best" an the results were...

[@blackrifle6736]

@@micualex9799 *...less than optimal. Or an absolute disaster. Cheers!*

[@a.c.e.7568]

And if you look up the April 2003 issue of MOTOR, you'll find the 5-page "Understanding European DIN Wiring" article.

[@ToolDemos]

Great, thanks.

[@aswclassicsiow8588]

Nice one thanks for that just downloaded in pdf

[@a.c.e.7568]

@@aswclassicsiow8588 Unfortunately, I looked at that download the other day as well and it is different from the PDF download I have that has charts listing all the relay terminal numbers and explanations. Strange, I wonder where I got my download years ago, maybe from a forum?

[@aswclassicsiow8588]

@@a.c.e.7568 Not had a chance to look at it proper yet, I have a full list of the DIN 72552 numbers so will compare with that cheers anyhow

[@herzogsbuick]

i had never ever thought to use vise grips on full size battery terminals so i could use smaller alligator clips and test leads. my god. now that i've seen it, i don't even remember what i used to do. probably find a pet or small child to hold the other ends. brilliant.

[@ToolDemos]

Haha “come here kid, hold this flashlight.” I’ve put kids to work too.

[@69420maaan]

Wow, you really turned that into a 7 minute video and it was interesting. This... and a few other videos ive just finished of yours, got you the sub just for the simple fact that you are a good teacher and i wouldnt mind learning car stuff that i dont need to know but might help in the future. Great stuff man keep it up

[@ToolDemos]

I appreciate that, glad you’re here.

[@sethtaylor5938]

The resistor across the coil attenuates the coil's inductive kick when the coil voltage is switched off. Some relays used a reversed polarity diode to do the same. However the diode can slow the relay time in mSecs.

[@ToolDemos]

Thank you Seth.

[@enoz.j3506]

You say the diode would slow the relay time ,why would the relay time be a problem,as relays are inherantly slow anyway.

[@troubleshooter1975]

I take it you mean the release time? I suppose it can. You have to remember it is working with the resistance of the coil too, to dissipate the energy... Some cars have the diode in the fuse block. Sometimes there are diodes, like an ATM fuse, inserted from the top too (like a fuse).

[@sethtaylor5938]

added: "release time"

[@colinhamer6506]

Excellent tutorial video I've had to look up information to remind myself so many times but I think it's going to be with me for ever now I've just subscribed and hope to find lots of video's like this

[@ToolDemos]

Awesome, thanks Colin. I’ll see you again.

[@bobbg9041]

Oem relay, was probably made by bosch Bosch relays are the best. A relay is noting more then an electromagnetic switch dble pole single throw. I can wire a relay in my sleep. So if you think of it as a simple light switch and know what 2 pins trigger the magnetic coil and whats normally open and normally closed then you can trouble shoot and test a relay.

[@blackrifle6736]

*Absolutely! When it's important, Bosch and Hella relays are worth every cent they cost. Cheers!*

[@forresterickson6225]

Very nice. The internal view really helped.

[@ToolDemos]

Glad it helped.

[@raygale4198]

Lucas England had the same type of system to identify wiring, all those different colours and stripes on wiring have a specific function in the Lucas system. Brown - unfused battery feed. Purple - battery fed fused accessory. Green - ignition switched fused accessory. Red - side light switched accessory. Slate grey - feed from ballast resistor to coil (from memory) . Now you know why old British cars are full of green and red wires in the dash.

[@richardcrowell284]

International trucks here Australia came up with either a complete yellow or white wiring harness with small numbers printed on the wires. The main issue was after many years of degreasing and cleaning the numbers wore off. As an ex auto electrician, I tore my hair out trying to sort these old shitters out.

[@ToolDemos]

What a nightmare.

[@raygale4198]

@@richardcrowell284 I worked for Detroit Diesels in Adelaide as an electrician, occasionally I would get asked to help out the mechanics, Kenworths were the same all yellow from memory. 439 being the switched ignition and 30 or 31 being negative are about the only numbers I can remember, long time ago. Recently helped a friend out restoring a Peterbilt, same system.

[@kevincrosby1760]

@@raygale4198 I still get calls from friends trying to isolate an electrical issue with a vehicle. I'm a PBX (phone system) tech, which means that walking into the phone room in a large office building and seeing identical wiring feeding hundreds of phones is just another day at the office for me. I'm well past the point of being intimidated by unlabeled conductors... :)

[@raygale4198]

@@kevincrosby1760 Phone wiring is witch craft, PBX and exchanges doubly so. :)

[@chlordk]

You said one thing wrong: Bosch has been making automotive electronics for "decades". It should be "centuries".

[@ToolDemos]

Right

[@dtandfam8100]

Great explanation on this!

[@garagemonkeysan]

Great video. Nice memory technique. Love how you used various tools to make your electrical connections. Mahalo for sharing! : )

[@ToolDemos]

Glad you enjoyed it

[@stevenmoomey2115]

You should tell how a Three Pin Relay works, that’s on a lot of older vehicles. A lot of Professional and Amateur Mechanics get confused by them.

[@ToolDemos]

Watching one blink on the inside would be cool too.

[@twowheeledparadox]

But aren't those even simpler than modern relays? One pin each for the switch, the load and the battery. One terminal of each of those parts is grounded.

[@stevenmoomey2115]

@@twowheeledparadox Yes, 12 Volt to one pin, switched 12 Volt out on another Pin. What Mechanics don’t understand, is the Third pin goes to a switch that, Switches to Ground, “Negative.” Gets really confusing when old cars have Positive on the Body and Frame, Negative is on the Switched side. If you want to really get messed up, on 10 Vdc HVAC Control Systems, White is Positive.

[@twowheeledparadox]

@@stevenmoomey2115 Yeah, that's right. I have used both a 3-pin relay (really chunky and with a metal shell) as well as a modern 4-pin unit on our old motorcycle when it had a 6V postive ground system. The load was a pair of horns. 3-pin ones were better since I could get ones that were rated for 6 volts. 12 volt 4-pin relays worked too but only when the engine was running and charging the battery.

[@rotaxtwin]

Of course there is a relay pulling tool.

[@Steveuploads]

Can’t beat a good Mnemonic to remember stuff.

[@1BCamden]

Wow, I am so saving this episode, thanks

[@ToolDemos]

Glad you liked it.

[@gadgetdeez7069]

A lot of this information is misleading. There are 2 different kind of shunts on relays. The rare diode type and the far more common resistor type. The resistor type doesnt care if 85 or 86 coil termainals are positive or negative. Because you'll run into a resistor type 500x before you run into a diode type, its basically assumed that all relats have resistor shunts. (Thats the component in the relay that prevents large inductive flyback voltages on the coil control leads.). 30 is not always connected to power. There are a lot of cases where this is true. For example, window lift motors and door lock actuators commonly use 2 relays. 85 and 87a on both are connected to ground. 87 is connected to positive, and 30 on each relay is connected to each motor lead. At rest, both relays ground both of the motor leads. This acts as a brake on the motor if not anything else. When you apply positive to 86 on one relay at a time, you will make the motor spin one way or the other depending on which relay is being energized. If both are energized at the same time, the motor does nothing because both leads are shorted together while tied to positive. So, no.... You are providing a lot of misleading information... 85 and 86 are the coil. Polarity is not specific except in the very rare case that you have a diode type shunted relay. 30 is common, 87a is normally closed (87a is connected to 30 when relay is not powered.) And 87 is normally open. (When the coil is powered, the relay will connect 30 to 87) Because 30, 87a and 87 are simply switch contacts, they have no polarity and are not polarity specific. Just like any other toggle switch in existance. If you're going to put information out in the world to educate people, make sure you're not feeding them bullshit.

[@al_dente4777]

I've only seen diodes used for preventing excessive return amperage hammering from halogen lighting getting suddenly turned off

[@DrHarryT]

The charge generated by the coil when it is turned off is because of the magnetic field collapsing and it's called "back EMF"... I don't know why they used a resistor unless it's to absorb some of the energy but normally they put a silicon rectifier diode reversed biased with respect to normal usage [pin 85 negative] to absorb virtually 100% of the back EMF energy.

[@BuiltatBlackjacks]

If you have a "flyback current" from de-energising the coil if can jump the air gap between the contacts in the switch, eventually killing the switch. The resistor provides a lower resistance than the air gap in the switch so the flyback current just travels round the coil until it dissipates.

[@DrHarryT]

@@BuiltatBlackjacks "flyback current" and "Back EMF" are synonymous terminologies. [That is energy introduced into the coil as a result of the collapsing magnetic field.] The resistor is across the coil of the relay [which acts as an inductor as well] whereas a diode is commonly used and has absolutely nothing to do with contact erosion. That wear and tear of the contacts is addressed by using harder materials, I believe by adding tungsten. [I haven't research contact formulas nor have the inclination to do so.] The "Dr" in front of my name is there for a reason.

[@BuiltatBlackjacks]

@@DrHarryT exactly what are you doctor of? Because I was unaware you could get a doctorate in Auto electrics?

[@DrHarryT]

@@BuiltatBlackjacks I see, instead of addressing the facts presented the modus operandi is to attack the messenger. I've been dealing with electronics and electro/mechanical engineering ever since TI [Texas Instruments] came out with the first digital watch and calculators. [LED] You are in way over your head against massive technological knowledge and experience... I am a professor.

[@DrHarryT]

I just hit me as to why they installed a resistor, it is quite possibly for the PCM [Powertrain Control Module] to identify when the relay coil has failed and has gone open delivering a specific resistance to the PCM. However there should still also be a diode in parallel with the resistor to protect the controller mosfet in the PCM from the back EMF.

[@z8669zzz]

One of the items, WHY? Since I never knew that, great video!

[@ToolDemos]

Glad you enjoyed it!

[@MillGapFarms]

Your video was fed to me by the algorithm and found it interesting. Great job! Mill Gap Farms

[@ToolDemos]

That’s cool. Glad you enjoyed it!

[@lokiva8540]

Good video, but be careful about saying "large terminals to carry voltage load", when current is clearly what's meant. Quenching diodes are more effective than coil resistors, but they require a fixed polarity, and so are better designed into the socket base and fixed wiring, and not be made part of the coil module.

[@ToolDemos]

Good catch. I went un-scripted there.

[@robertarthurs328]

Don't forget 87a

[@ToolDemos]

Right

[@therealdisston]

Thanks. Clear and concise. New subscriber.

[@ToolDemos]

Thanks for the sub!

[@treeguyable]

Never knew there were " retractable test leads" out there. Got my 2 or 3 jumbles of wire, with alligator clips on, wrapped up in my electrical drawer, for over 40 yrs now. I go to amazon now, when looking for new tool ideas. Things have changed a lot, since my days as a Mercedes Benz tech, 30 yrs ago. I did break down, and buy a nice set of Knipex channel lock style pliers.

[@ToolDemos]

I really like using that test lead set. It makes life just that much easier.

[@treeguyable]

@@ToolDemos No kidding, coulda used those decades ago! May still get a set.

[@jimnaden5594]

Another excellent source for tools is Summit Racing. Excellent stock and selection, some less common items ship straight from manufacturer. I've had sets of the pull out leads for well over 20 years.

[@danburch9989]

The video didn't actually say WHY they were numbered that way, just that the Germans did it that way. Did I miss something?

[@ToolDemos]

Amazon Affiliate link to the OTC relay pliers: amzn.to/3ybQeii If you click the link, it supports the channel, but won’t cost you more.

[@douglasnsarkoh6998]

Please I need relay plier for my self

[@blackrifle6736]

@@douglasnsarkoh6998 *OTC 4493 Angle-Tip Relay Pliers. Now you can go find them, but nobody's gonna gift them to you. Cheers!*

[@KF-bj3ce]

Now this has answered my question of why the odd numbering sequence. Thanks for this and obviously you understood my sleepy night time comment.

[@ToolDemos]

Glad to hear it.

[@ThePszczolkarz]

Great video! You really nailed 'why':) Nice to see how it works! And nice trick to remember this german chaos;) Thanks for sharing!

[@ToolDemos]

Much appreciated! 👊🏼

[@mikevanin1]

Sorry Steve, your video doesn't answer your own question. You simply tell us WHO numbered them, not WHY. Why are the relay coil connections not numbered 52 and 53? Why are the contact connections not numbered 10, 15 and 122? In other words; WHY did Bosch number them that way? Your "half-answer" basically says "They're numbered like that BY Bosch and I have NO IDEA why!" There are, in fact, real answers available on the web. Even for this question! Allow me to digress! Caveat lector! Automotive "standards" are notoriously obscure, antiquated, and particularly stupid in many cases, being "defined" by people often unqualified to do so. These are the reasons why shock-absorbers are called "springs", dampers are called "shock-absorbers", contacts are called "points", capacitors are called "condensers", transformers are called "coils", alternators are called "magnetos", nebulisers are called "carburettors", and the main power switch is called the "ignition" switch. And then we keep the quaint terms of "dashboard", "fender", "dipping" our headlights, "throttle", "airbags", "transmission", "hood or bonnet", "trunk or boot" ... and so on! My favourite term worth deriding is "spanner", Americans say "wrench", a word to mean VIOLENT twisting - not too inappropriate- yet still funny. But the British "spanner" is derived from the similar German word, which meant "tensioner" - it was the small tool used to tension the spring of the hammer in early flintlock--fitted firearms. Earlier firearms, using the "matchlock" (a piece of smouldering rope called the "match") needed little force to swing the match into the "pan" that lit the gunpowder feeding the main charge. But flints needed to be sufficiently firmly "struck" to produce a reliable spark! Even then, if the careless or hurried bearer hadn't ensured there was enough powder to go all the way through the touch-hole into the breech, the powder in the pan would flare up with no following "boom" from the main charge - and all you got was "a flash in the pan"!

[@aswclassicsiow8588]

look on the net under "DIN 72552" as this is were the numbers come from and you will see why each number is used

[@ToolDemos]

Well said. By the way, if you decide to start a channel about etymology, let me know. You would be fascinating.

[@aswclassicsiow8588]

@@ToolDemos Dont even know what that word is/means??????😄😄

[@albanana683]

@mikevanin1 I'm not sure where you are getting some of your word equivalences from. I've lived in the US and the UK and worked on cars since the 1980s. I've never heard anyone confuse shock absorber and spring. And a magneto (producing high voltage energy for a sparkplug) and an alternator (producing charging current for a battery) are wholy different things.

[@mikevanin1]

@@albanana683 Of course they are different, Al, but only in the automotive world - my point exactly. A magneto generates one Alternating Current cycle of high voltage to feed the primary winding of a transformer ("coil") which induces an extra-high voltage in the secondary winding, to jump across the spark plug (originally "sparking plug"). I'm not saying the words are misunderstood or confused these days - I'm commenting on how POORLY the vocabulary used in the automotive industry was developed! In engineering theory, a spring can be used to absorb shock - which is what they do on vehicles. In engineering theory, dampers are those devices that are those poorly-named "shock-absorbers", which absorb no shock and merely distribute, or dampen, the spring action over an extended period. But it appears you've missed my point. We have to live with this crap - we can't easily change our language to "perfectly" defined terms that ALREADY EXIST! Language naturally deteriorates - we think it improved because of all our technical words. But only the pedantic and the precise speakers are bothered by it - everyone else doesn't care "two hoots".

[@MadScientist267]

This has been a long standing question and came up some 30 years ago when I started calling those "87 relays" That said, I know what is what just looking at the relay, but couldn't tell you what they are by number lol

[@GameBacardi]

Out Off Topic - If you want replace original Bosch component (ex. relay) or you can't find original component anymore, and want you another brand, remember, some replacement components have quality issues. Sometimes, cheap relays broke or are weak to work. One car mechanic demonstrade with fuel pump relay between Bosch and another cheap brand. It had different coil size (mH) to compare Boch version.

[@ToolDemos]

Thank you. Cheap parts are everywhere and cause so many problems.

[@blackrifle6736]

*You omitted one word: Chinese. Cheers!*

[@uxwbill]

Now I've discovered a new tool that I absolutely need! (Yes, I appreciated the explanation. I too had long wondered the same things. Another sidebar: I wondered if you might not wire up the relay to buzz.)

[@ToolDemos]

That would be fun, but the majority of my audience wouldn’t give two hoots about that.

[@blackrifle6736]

*If a DC relay buzzes, the coil is getting an AC voltage from somewhere in the circuit. It should not be there. Cheers!*

[@coolcatsgarage558]

Thank you brother! Great info

[@ToolDemos]

You’re welcome. Thanks for the feedback.

[@christianvith6217]

In Germany or Austria, all those who want to start working as a car mechanic (or automotive technician) have to attend the so-called Berufsschule once a week. Everyone has to learn these numbers (called Klemmenbezeichnungen) from the very beginning, and you can be almost sure there is at least one test about these numbers in school.

[@ToolDemos]

A mechanic who understands the systems he is working on makes better repairs.

[@daryllect6659]

Cool pliers!

[@dave-d]

Wow. Actual facts. Careful dude, you'll break the internet. Respect.

[@ToolDemos]

I appreciate you.

[@user-rr6gr7og9q]

What a brilliant video Thank you for doing this

[@ToolDemos]

Thanks, I appreciate that.

[@jimlelan4906]

What a great video! Thank you very much!

[@ToolDemos]

Glad you liked it!

[@cynic-al]

It generally matches the wiring numbers on industrial power contactors, accessories and control relays too.

[@LariFariYoutube]

Thats a excellent explanation.. Thanks for uploading.. Greets from Germany ;)

[@ToolDemos]

I appreciate that. Now I wonder how bad my attempt at pronouncing the German words was.

[@jackfarrell4727]

Great information, thank you

[@ToolDemos]

Glad it was helpful!

[@glennappelgren5492]

Great video ! Thanks for doing it Glenn , Sweden scandinavia

[@ToolDemos]

Thank you Glenn, I appreciate that.

[@sylvainlessard9999]

87a is used when you want to disable something. e.g. Starting inhibit when engine running is the most common function I can think of. The starter control circuit was running through pin 30 and 87a. The pin 86 was pinned to alternator. Safety interlocks were using that a lot too.

[@maxhouseman3129]

In industrial automation, the first number represents the order of the contact: 1, 2, 3, 4. The second number represents the type: 1/2 normally closed, 3/4 normally opened. That system is simple to memorize. I am pretty sure that the IEC/EN/DIN rules that.

[@ToolDemos]

Sounds easy

[@chandrakantindapurkar8738]

Good information in simple words Thanks a lot Sir..

[@ToolDemos]

Glad it was helpful. Cheers!

[@robertmccully2792]

The curse of wanting to know why. Had that all my life.

[@ToolDemos]

Then, when you do find out, you want to tell somebody. They usually end up falling asleep on you.

[@blackrifle6736]

*Curiosity is never a curse, always a blessing. That is why mankind advanced for the last 100,000 years. Cheers!*

[@kennethwoods9804]

Good to know, I deal with these alot Thanks !

[@ToolDemos]

I appreciate you.

[@jrpeet]

Really interesting. Didn't know how relays worked

[@ToolDemos]

I hope I helped your understanding.

[@Hackenberg]

Going from military aircraft to automobiles has been interesting. Thanks for the explanation.

[@ToolDemos]

You bet. Thanks for serving.

[@NemetskyCzar]

Nice. Great explanation.

[@ToolDemos]

Thank you!

[@deanrhodenizer938]

Thank you. I was always a bit bewildered by the numbering scheme - thankfully most of the relays I used (for my own purposes) had the diagram on the outside of the package.

[@ToolDemos]

That is helpful

[@r.castano4325]

30Amp = power source connector Pin 30 Nice tip. I recommend you add a schematic diagrams: SPST, SPDT, the control circuit you built for the demo. Add these definitions: P = Pole, T = throw, NO and NC. After teaching control systems for 30 years I can tell you that NC is better understood as Normally Connected, and NO = Normally Off. Because the word closed in the vernacular is and always has meant access denied. hope that helps

[@ToolDemos]

Great tip, thanks.

[@dido1803]

Great information!!

[@ToolDemos]

Thanks

[@tracker335]

Wow this is good . Subscribed !

[@ToolDemos]

Awesome, thank you!

[@AdrianJayeOnline]

Awesome tool

[@whitelion7976]

Am in Africa and have problems with relays all the time. Thanks for explaining that.

[@ToolDemos]

That’s awesome! Thanks for your comment.