VEHICLE RELAYS - Operation & Diagnosis

If you've ever wondered what a relay is and how it works, this is the video you've been hoping for... Other information about the FET book is at www.brighterideas.com

[@81eagle]

Hands down the best video on relay function I have ever seen. And shown way better than I learn at tech school.

[@bivideo7]

Don't misunderstand - I wasn't criticizing. I was trying to point out that in the end, the solution was very simple, compared to the idea of a mis-wire. You did a great job and should be proud. Your future successes will be largely a result of you never forgetting this experience, and the next time you have an electrical problem I hope you'll go out expecting the simple answer. This is a critical moment - this could change your expectations and change your life. Seriously. Again, good job.

[@Northropfam]

This video is a nice change to the many fall short videos I see on KZbin for automotive repair. I never thought about splitting the circuit much at the relay but this is genius. Most of the time in the past I've just removed them and manually jumped the contacts or coil to see what happens and where to go next in the circuit. This is a much better way to go. This guy definitely gets it. I'd like to see what else he has to offer. :)

[@Bevoin1970]

I never quite understood how relays worked, now thanks to your brilliant video and explanations, I have grasped exactly what goes on now. Many thanks.

[@Diesel1Dee]

i just got this book a few weeks ago. it actually is great. quick diagnosis of components and systems. im an apprentice truck and coach tech and its helped me quite a bit. cheers.

[@sesetlhi]

You are brilliant!! That's the art of teaching. I now feel confident to take on wiring challenges on my car. Recently bought and installed a "coming home leaving home module" on my car, and had a problem with the dimness of my lights when unlocking/ locking the vehicle. I even resorted to using LEDs on the fog lights. But now I know the problem was with my wiring - I need to run the module through the car's headlight relays and not directly to the lights. And after watching your video (although you used the horn as an example), I now know how to rewire the module. Thanks a lot

[@gregorrobertson4544]

Been looking for this stuff for 50 years. Not too late! Because still working in this field. Well done. If you're ever in Edinburgh I'll buy you a couple of beers!

[@bivideo7]

No prob. Keep at it. Teach anyone who will listen...

[@sevinhendryx578]

I'm going to school right now to become a mechanic and this video has helped me a lot. Due to the fact this is my first time learning about electricity and how to diagnose electrical problems in vehicles. This video has made it a lot easier to understand relays and diodes. Thanks!!

[@chawkinouizi9128]

I love watching people that actually know what they're doing ! Thank you its been a great help for me.

[@h22sparkle]

I like how he explaines this theory in detail which brings a lot of electrical issues to light. I wish I would have learned this in highschool.

[@bivideo7]

Cool - Manuel bought the manual! Let me know if you have questions. If you help the teacher learn these concepts you'll both be better off. Be generous and understanding of his need to not feel threatened. Remember to ask a lot of questions and always give the teacher(s) a chance to save face. Keep up the good work.

[@manuelvaleriano7789]

thank you Dan. I learn more from you than I do at school. I am currently taking auto tech at the local community college. I recently purchased your load pro with the manual.

[@SouthMainAuto]

Hey Dan , I'd like to use this video again as a reference in one of mine if you don't mind?

[@micsor4121]

May your Blessings be hundred fold. Thank you Dan. Awesome

[@bivideo7]

mic sor Thanks. I'm glad it helped.

[@AlmalikyAli]

Sir, you are a great teacher. May god bless you.

[@carlbarnes4293]

Where have you been all my life!!!!! This is hands down the best explained relay video I've ever seen!!!!!! Thank you for taking the time to explain it!!

[@bivideo7]

Starting in 1961 - GA, OK, IL, GA, TX, GA, IL, OK, MI, NC.

[@carlbarnes4293]

+Daniel Sullivan I wished I could have met you when you were in Texas! I have learned more watching your videos today than any overpaid electrical class I've attended!

[@capedoryus]

Nice Work Dan, The production is first rate. Love the green screen and content is great. I can see why it has almost 200k views. Thank you for all the work that went into this production. PS It did work and after 61 years I understand relays.

[@pclutch]

This is why KZbin is awesome

[@vemlacduong1954]

Thank you for sharing this knoledge . This helps me to understand my study .God bless you and your family .

[@makalu877]

Daniel, you are a great teacher, thank you so much for posting.

[@kevindownes2543]

Hia again Daniel. Re-checked the wiring diagram on Autozone, and the 5 and 3 are inversed! Rechecked after having re-drawn my rely circuits and have found the problem in the steering wheel clock spring! (As you marked in your tutorial - check the polarity of the connections before starting!!!) Thanks again, and you're really an excellent prof! Cheers!

[@mattwaldrup4300]

Wow! Very informative. You explained it in such a way a dummy like me can understand it. The visual aids are great. I've always struggled with relays for years. Thank you very much

[@kevindownes2543]

As you say, the solution was simple! But in my defense, the horn has never worked since we've had the car, and I thought it could be a possibility that the car was repaired after an accident and just wired up wrong. (Barking loudly up a very big, but very wrong tree apparently ;-)) Have got a colleague repairing the clock spring as we speak, so should all be good for the weekend! Thanks again for all your help!

[@07aussie1]

thanks for your very detailed drawings and explanations to put it all in better perspective. I'll continue to study.

[@bivideo7]

You're welcome. Take this success and build on it. All relays work the same way. Make sure you watch the video about testing from the relay base. Keep up the good work.

[@edwardlopez30]

Wow , kick ass notepad illustrations !!!

[@bivideo7]

Awesome - I was going for totally kick ass, but plain old "kick ass" is still good. Thanks.

[@enoxosr1]

The main reason to use a relay rather than a standard switch is to isolate the two circuits mentioned in the video. For example, a horn requires a circuit with a relatively large current in order for the load (horn) to sound (this current flows in circuit 30-87 or 30-87a). This current is isolated and controlled via another smaller current in the 85086 wires, which actually control the coil (electromagnet) of the relay.

[@jschmadeke4life]

Awesome video! Thx for explaining the diode concept.

[@AstronauticxGV]

Great presentation and very, very pedagogic ! Comlex electronics explained for simple understanding ! Even my 11 year old son has become a Sullivan enthusiast !

[@willlyte975]

Absolutely brilliant! Thank you for sharing

[@electriciandallastx9182]

Thanks for the thoughts you have shared here.

[@celtichongy]

Dan, excellent videos and content, thank you for taking the time to share this useful material online.

[@tonywilliams7918]

Thanks Dan. Graphics, Details, Examples, Explanation's, Pace. I appreciate the tutorial and will subscribe!

[@bivideo7]

No prob. It's what I do - when I can. Can't afford it now, but hoping to start over soon.

[@bivideo7]

It's way easier to pull out a relay that costs the manufacturer about 5¢ to manufacture when those contact points fail than it is to pull out a horn switch buried in the column when they fail. Every time you sound the horn, the coil in the horn stores energy that's released back into the switch when you open the circuit. That energy arcs the point and that switch stops working. A manufacturer does what is does for 2 reasons - easier, or cheaper...

[@actyon20]

Sir ! YOU AR THE REAL MVP ! I can't thank enough

[@luzgonzalez2838]

Great video! I"m residencial electrichian and it help me a por.

[@observersnt]

SIMPLY, excellent. Thank you

[@bivideo7]

The only way is voltage drop. I recommend LOADpro or Relay Buddy. Turn the load circuit on and test the voltage drop at the component connector. Or use the Relay Buddy which cycles the relay and measures drop across the contacts automatically. The best method will always be to test the circuit under load. I know people want to ohm out the contacts but it's hard (gotta energize the coil) and not very effective. Remember, the ohmmeter is essentially a sucky diagnostic tool.

[@sansei818]

GREAT Video. You did an EXCELLENT job at illustrating how a relay works. Thanks

[@bivideo7]

Thanks. I'll assume you did a GREAT job watching the video that did a GREAT job illustrating how a relay works... Takes two to teach and learn... :)

[@michaelr.cornett2423]

" Touch'e.. Daniel... I really didn't give two shits about relays until stumbling across your web posting. Nor do I have a desire to further my relay education. However..... I do have a thirst for for knowledge, and you did such a great job sharing "your knowledge ", that I just had to thank you... So, Thank You. I look forward to learning more. Best Of Luck, Mike

[@johnschmidling1624]

Hi dan your video is great I also purchased your troubleshooting book it was a great help when i completed my final in school

[@h22sparkle]

in one of your segments in this video at 5:26 you spoke of the horn and the relay. I had a similar issue with my dodge neon and it wasn't the wiring or so I thought. It came down to it at first after I got it to work. Then shortly after that not only it was the relay in the car in the cabin but the switch attached to it. Everything else was okay. I kept on going through the headaches of driving everytime I had my headlights on my wipers activated which meant that switch was bad and making continuity somewhere else.

[@chocOneOOne]

This was very helpful as I've never used a relay and I'm trying to use one to wire and LED strip to function with the door open/close without just tapping into the dome lights. It's a little different because my negative coil would be tapped to a ground that isn't active when the door is open I need to use 87a as my switch on so to speak and 87 isn't needed at all - not sure if this is possible. I'm making this way harder than I need I'm sure but I'm determined to figure this out..if it's even possible the way I want to do it.

[@rxe9231]

Very informative details Daniel, Thanks for this information. I'm having problems with replacing the Denso FB257H OEM flasher relay with a 5 pin as you use in your teachings. I am exchanging because I've installed LED flashers. The system is fitted on a Kawasaki VN1600. The FB257H has the terminals arranged in two parallel rows 3x3-1=5 (no terminal) I am not able to determine the correct connects and keep blowing 5amp fuses. The replacement relay was brand new and while I try and get the correct information, I'm running with the OEM unit but this generates a faster flashing rate, as in fault. Are you or anyone else able to provide a suitable solution please?

[@bivideo7]

Yes - if you realize that for a relay to switch a component, that component has to be connected to the relay - usually terminal 87. 87 is at the "top of the T" when you lok at the relay base. Voltage will (usually) be at terminal 30, and you can (a) read voltage at 30 and load it, (b) read resistance to ground at 87 (usually less than 300Ω), and (c) use the ammeter function to just from 30 to 87 to run the component. Mechanics "go to the part" - electrical diagnosis is done at the test points.

[@im7401]

I like your name. We might be related, Brilliant vid everything I needed to know about relays, not sure I will remember it all but will definitely watch this again if i need to, got here from SMA

[@MateusJaguar]

Thank you very good video. Question: What is the fifth middle prong in the center of the relay plug teeth?

[@ozzstars_cars]

Excellent explanation of relays, thanks for the video

[@T3vAJT5N]

extremely well done - many thanks

[@bivideo7]

That happens - it isn't very common, but it happens. Hope you were able to benefit from any effort you put into the harness inspections (if you did them). I still contend that the 80% rule of wiring is the best way to start. The odds suggest you'll have the best results by assuming wiring, but there will always be the 1% ECMs. Hope I didn't mislead you too badly.

[@coldpak82]

Great Video, I'm dealing with a Auto-shut down relay next to a Fuel pump relay there no Action with power going to fuel delivery or anything.Question if you pull the relay out.In the recept-part should I have a Ground and a Hot inside the female recept- part ?

[@bivideo7]

No problem. Remember to split the problem with a relay with the cover off.

[@How2Wrench]

Awesome Lesson...This guy totally trumped mine. I look forward to sharing with future students.

[@bivideo7]

1) Not always, but it will *usually* connect to the load and then to ground. There are times when it can be otherwise. The Key is to understand how it works, and not try to memorize a specific pattern. 2) Sometimes, but not always. Depends on the system. Sometimes the coil wire will simply be a jumper from 30 to the coil behind the relay panel. Choice is yours, as long you know the 2 circuits are separate. 3) Depends on diode if there. Diode will always "point to positive" if across a coil.

[@JorgeRodriguez-or6pz]

I bought an 02 gmc sierra 5.3 v8 recently and the guy who sold me the truck had someone replace the fuel pump and the gauge in the dash that indicates the fuel level in the tank, so the truck worked fine for a while but one day it stop as I was driving it and when I tried to start it again it would not work after i tow back home I checked the fuses and the relay and find one for the fuel pump bacwards according with the guide in the fuse box so I flipped back and crank the ignition key and the engine turned on and run for about 5 minutes and stop again I thought that the relay was burnt so I bought a new one but had no luck so I'm wondering if they installed the relay bacwards and mess something else

[@kevindownes2543]

Hi Daniel. Thanks for the excellent tutorial on vehicle relays. I'm not scared to attack the problem now! However, I'm trying to repair the horn circuit on my wifes Corolla (2001). I've performed all the tests, and have the following results (ISO Relay): 1 - 12V, 2 - 12V/Open Circuit horn pushed or not(!), 3 - 0V, 5 - 4.5Ohms. I opened the relay and the horn sounds when I push the contacts together. I checked the relay with 9V battery and it works OK. Relay wired wrong in the box? Please Help

[@littlegoobie]

quick question about relay pin outs. I see a ton of them online of varying prices and brands. I would like to try out some of the less expensive ones (5 for $15) but i'm not sure it's just pull the plug, replace, and go. Are the pin locations/numbering standardized on most of them? this is for a common aftermarket relay, not a proprietary type that would plug into a fuse block.

[@ICHLIEBEmusic]

very informative video! great drawings too! my car will crank but not start I have 87 Porsche 944. new battery and new fuel pressure regulator but wont start. If i spray starting fluid through the air intake then it does start. what should i check for next?

[@johnalexander4940]

loved your video man fast and 2 the point.

[@nandsharma4021]

Hi, thanks for you in depth explanation. I do have a 2003 buick lesabre that has a power trunk that is no longer operable. It has two fuses and a relay that are related to the power trunk. Both fuses are good, one was blown before and I replaced it. The question I have is can you reverse a relay, I mean can you yank it out and spin it 180 degrees and if you can what are the consequences.Finally what steps should I take to solve this problem. Thank for you help and instruction.

[@jetmelt]

Super teaching! thanks!

[@crackatinny]

I'm trying to wire up a solenoid for my Laycock overdrive, I done some research to discover to replace an old Lucas relay with an off the shelf box type one the conversion goes as follows, W1=85, W2=86, C1=30, C2=87. Now have wired as shown in my Vanguard workshop manual (but using the conversion above), when I hit the switch I get a burst of current then its gone even though switch still on, my first thought was blown fuse, but turn off switch and turn back on again and you get the burst of power then nothing, this is from terminal 87, here is what I find odd and makes me question the conversion, through terminal 87a there is constant power even with switch and ignition turned off, any ideas?

[@aquaholic38]

awesome video and very informative!!! it help alot. thanx!!

[@1tupaijet]

oh man..this tutorial helps a lot. thank you

[@haslsmiley72]

HELPFUL! Thanks..

[@HAWAYP]

Thank you for your reply, my point is that besides the understanding, for the number 1&2 question, if the 87A pin is connected to GND and load/coil have the same Vcc1 then it will always be a flow from 30 to 87A and the horn will always be on unless 87A is loose but it could damage the system,but if we connect Vcc2 to 87 and the horn to 30 and 87A grounded with the load, the only flow would happen only when the horn bottom is pushed and both circuits would be isolated.please let me know.Thanks

[@ann569]

Thanks for your easy to understanig, practical demo

[@giga069]

Thank you for the very useful information. :)

[@Viper81766]

Great video. Can I test "voltage drop" through the relay box ? I have your book and test leads and both are amazing. Thanks for the videos, book and test leads.

[@H20RIDER]

Terrific explanation and video presentation. Question: why would a relay flip with a 9 volt..... but then not function with the 12 volt in the vehicle? I'm trying to get a hi-lo beam dipper switch sorted out on a old Triumph 650 (pos. ground). Battery, bulb, and wiring test fine. Relay just won't flip. Thanks for the videos and any ideas about this prob.

[@SAJTV]

very helpfull video really is.. thanks for upload man.. you are a star..... i got a question bro... do you know where is the alternator wire in bmw 320d 3 series? that is coming to battery? is it also passing through trunk by any chance? actually i am installing secondry battery and a split charging replay switch. i am looking for a 12v ignition wire. which only powers when we twist the key twice. by any chance is that wire somewhere in trunk too? please help. many thanks.

[@Leo_Berger]

Thanks man. Very good movie.

[@RapAndChopin]

Awesome vid, but I have a starter relay on my bike that I thought was blown because I tried to jump it with a car that was running (should have turned the car off) so anyway it doesn't work, but I can still start the bike if I take a piece of metal and touch both bolts on the top of the solenoid so that the current flows through them. I replaced the solenoid but it doesn't work, and I have to do the same thing and touch a piece of metal to the bolts on the top to engage this. any ideas? thanks!

[@TheAbepalihan]

In your summary you measure system voltage on terminal 85 and ground on terminal 86. Are those backwards? For an AC clutch scenario the pressure sensors and WOT would close the ground side on terminal 85 and battery would be on terminal 86. Battery go on either 86 or 85?

[@meti903]

hello sir i have a car that randomly hasn't been starting specially when its cold it cranks but wont start i have narrowed it down to it being the ecm relay because i got a code for it saying low voltage on that relay, so as you might know intermittent problems are hard to reproduce, so i remove the relay same think happens the car don't start i put it back in and it starts so now i know my problem is right there, but my question is i have tested the relay with a dvom the relay closes when i energize it and it has continuity' so that confuses me alot i guess it means the relay is good, i would like to know maybe when its cold the relay sticks and don't close because when this happens if i keep trying it after 4-5 times the car starts i hope you understand what i'm trying to ask thank you in advance.

[@bivideo7]

BTW - I'm sorry to sound like a commercial, but all of this info is in the 200 page shopbook I wrote on electrical diagnostics. There's a short video on my channel about it. FYI.

[@joshboab7160]

keep up the great work

[@VojvodinaNet]

Thanks, well done!

[@BartolMagProbe]

Great video! You hit it right on the head.

[@mrdyoung0519]

fuel pump rely location 2007 mercedes c280

[@xodrinker]

Superb, thanks!

[@richardkidger0250]

Awesome, I have the book in the U.K.

[@ramon440icu]

Super good teacher...

[@usdms13]

awesome explanation!

[@alvadaro]

Hi, I followed your indications to mount in my car and electrical fan with a relay, but i did a little mistake , I put 86 in 85 and worked ok, after I tried to put a 2nd elecrical fan and I saw the mistake, I put wires according indications and the electrical fan worked slowly,so I had to go back. Question is Why did Ef worked slowly? Thanks a lot.( I use a relay wit a diode and when I went back diode turns on.)

[@stradastudio]

Very informative , Thanks, have a problem with a Nissan 300ZX horn has been going off in the early morning and evening starts small like a barely perceivable blip and the after a few minutes locks on to full blast. End up having to pull the fuse for it to stop. Could this be a faulty Horn relay moisture Bridging the contacts or such

[@bivideo7]

Where do you live?

[@stradastudio]

Auckland , New Zealand . Just coming out of winter, still very wet.Daniel Sullivan

[@bivideo7]

***** I'd assume contraction of the material in the steering wheel, due to the cold, closing the contacts. Same thing happened to a car in the apartment parking lot during college. It could be the same thing inside the relay too, assuming it's defective in some way.

[@lalanx5]

comprehensive explanation

[@darren115]

top video!!! makes understanding how relays work much more simple. 5*

[@getreadytotube]

Great video. And you did it in plain english too!

[@martinguitarhd28]

If i use the loadpro at terminal 30 and ground lead of meter at batt negative and load it and get a good voltage drop at the base .Do i need to read resistance to ground at 87 and use the ammeter from 30 to 87 to run component ? I'm guessing i would have to do all the other checks as well to make sure all the other connections are fine or am i missing the point and don't need to do all the above.

[@antegas]

We say in spanish "Demasiado bueno" or Excellent video. Thank you very much sir.

[@georgekofiackon6399]

Very good presentation

[@ahmedbig1356]

thank you Dan

[@sudilos1172]

Awesome

[@evoBOT2006]

your awesome!!!

[@afrosamuri05]

great vid dude, when i was doing my auto elec apprenticeship I had some dumb Portugueeza dunce for a boss trying to explain the operation of relays to me with little clarity

[@SouthMainAuto]

Hey Dan is it ok to share this video on my channel or make mention and link to it?

[@bivideo7]

Sure - go for it. Anything to help.

[@SouthMainAuto]

Ok just wanted to check to be sure. Often when I am talking about diagnosing I check the relay and it would be nice to refer people to a good video that shows what a relay is and how it works. Avoid people thinking it is a magical box haha.

[@SouthMainAuto]

Hey Daniel Sullivan, Just a heads up I put together a video that will be published on Apr 10, 2015 @ 8:00am. I tagged this video in it and put a link to it in my description box too. It is a video on an F-150 , no start , no crank , no communication. I think this will be a perfect fit. Have a look when it comes out let me know what you think. Thanks again --Eric O.

[@rodrigomedranof]

MAESTRO !! MASTER !!

[@Texmexifly]

What is the purpose of 87A. The normally open position. I would have thought the magnetic switch when not being pulled down by the coil, i.e. being in use, it should be resting against a non conductor. I'm wondering why the metal conducting tang?? Where does this go to? Really enjoying your book. Thanks.

[@bivideo7]

Whatever you want. Often used in headlight circuits for low beam - N.C. - then the high beams will be on when the relay is on - N.O. There is no answer other than "when you need a normally closed contact..."

[@Denkha94]

Hi their I have a standard 4 pin 30 amp automotive relay. the points are 87 30 86 and 85. would the 86 pin on the relay be ground? thank you.