Voltage Drop Testing With A Test Light? [Part 2]

[@VitoVeccia]

Personally, I always used a headlight bulb to put a good load test on the circuit. Learned that the hard way at the GM training center. That's when I learned the difference between static and dynamic testing. Some of the best knowledge I got was from there. Always do a voltage drop test with the meter, in conjunction with the headlight bulb.

[@juansamudio5870]

Personalmente llegue a utilizar 6 headlight bulb para detectar problemas con la bobina del motor de arranque, para poder diagnosticar una falla dificil

[@joedavis2081]

I have used this test many times, I modified it a lil by using my meter with my test light to get a voltage reading, excellent test.

[@3TsMOBILEAUTOMOTIVEREPAIR]

I have to agree you 100% nearly 20 years I’ve never had an open motor with a bad power or ground curcuit. Not saying it couldn’t happen. But if your any tech you’d know the power or ground can back feed through a motor or clutch coil. Good explanation and visual. Thanks for what you do @ScannerDanner

[@DestinyOkoh-co1lm]

You really give me confidence to do electric work

[@ScannerDanner]

Awesome! That is great to hear

[@memery301]

Beating a dead horse? It doesn't matter how you explain it some people just won't get it. Very good content. Keep the kiss method.

[@wyattoneable]

It's always good to have a refresher. Thanks Paul.

[@spelunkerd]

Your career experience is solid information and I love practical remarks like that. In the AC world it is not uncommon for motors to die as a result of voltage drop in the supply line, although I don't know about DC automotive fuel pumps. It took me a while to understand why for example an AC well pump might die as a result of inadequate voltage from upstream or downstream electrical line resistance. When AC motors get inadequate voltage, they respond with the only thing they can do, demand more current to build enough power to overcome startup torque. That higher current for longer time leads to the tiny wires inside the windings getting hot and the motor burns up after that. To make things worse, the duty cycle of a motor getting inadequate voltage makes it work even harder for a longer time to meet demand. So, wise electricians may do a quick check of voltage at the new pump when it is working to reduce the chance of damage to the new pump. I hear you when you say that high current light bulbs aren't necessary for automotive diagnostics, but it is so easy to do that check, so why not?

[@jimpetty2961]

i was just rewatched your video on test lights the other day long time subscriber i learn alot from all you guys thank you

[@ScannerDanner]

I've studied this strange phenomenon. Not sure the difference with the AC and DC motors offhand, but this explanation makes sense: low voltage to a motor, equals less counter emf (counter voltage) the motor will produce because it is spinning slower. This is what limits current flow. The slower the motor spins, the higher the amperage. There are variables to this of course. But I've not seen a burned up brush type DC motor with the cause being a low power feed or good ground. I would say that if I had repeated motor failures on a circuit, I'd definitely be testing the power and ground with a little more scrutiny. But I don't fault those who like to add additional loads. I just trust my meter and my test light results, so never had the need to go beyond these two tools.

[@andrew7202]

Seeing these concepts in the field for the first is definitely crazy lol, when I started really doing voltage drop tests and understanding how and why they work was awesome. It never clicked till I started watching your videos so thank you. It really hit home when I got done watching your videos the one night just so happened had a now start issue on a boat motor and I applied what you are talking about now and saw it like instantly. Grant it I was lucky where I started but still seeing it and going holy shit I have a bad ground and now was looking for and found. My god it was a fantastic moment since I knew I had learn this but also it was sick seeing it all happen and how it did. It was so cool making it have voltage and not have voltage on the ground by simply tapping and untapping a broken wire on a ground bundle. lol I’ll never forget that day and how it all made sense. SO THANK YOU DANNER!! Anyone and everyone I meet who is thinking about getting into this field I tell them go watch you or if they are in the field I tell go watch you. I have learned so much.

[@ScannerDanner]

Fantastic moment indeed! And one you can visualize and fall back on to help you with other similar issues. Good stuff man, thanks for sharing!

[@markjohnson8162]

I use this test for many actuators , windscreen washer pumps, fuel pump regulators, fuel pumps , and so on

[@throttlebottle5906]

combine a test light and/or light bulb with the meter in parallel, combined voltage and load test. you could also parallel a wire wound resistor of appropriate value with test light or meter. all sorts of variations work for better testing information.

[@dwightschrute1953]

good you see you again bro , I've been testing voltage drops with a test light for years 😊

[@tsmith578]

Went through a bit of a similar situation with my friends 1995 Dodge 2500 truck last week, It has a bad connection with the main battery ground connection at the engine block, The engine still cranked over and started, But it was pulling excessive amperage through the body ground strap between the firewall on the rear of the driver side cylinder head, and overheated the ground strap so bad that it melted the coating off of it. Thank you for another great video Paul.

[@darinjohnson7280]

Thank you for all you do for us, Paul! I’ve made a few “noid lights” with various bulbs with wire leads and small T-pins to plug into circuits to load test, I usually use one that has a 9006 halogen bulb. In my earlier days, have been fooled a few times with a volt meter before I understood that a circuit needed to be loaded..

[@johnreid859]

Seems simple. Thanks Paul.

[@wingman8447]

Good lesson.

[@astrogate1]

Awesome lesson and very helpful thank you!

[@paulfiebke3909]

Thanks for showing us this keep up the good work

[@whitetiger8652]

Great explanation.

[@rdaleyj1]

Awesome simplifying sir, thank you. 😊

[@JohnSvensson-j6m]

Excellent tutorial scanner

[@sheerwillsurvival2064]

Always great information and training. As always these are golden 👊🏻👍🏻

[@GroundedDiagnostics]

If the horn was good and the wires couldn't support the current flow you would see it with your meter or light as voltage drop. Thanks for all you do Paul.. 👍👍

[@isalmankhan1]

Yes most awaited video of the week😍😍😍 Thanks for sharing SD👍🏻👍🏻👍🏻 Please share some latest case studies with James Danner😍😍😍 Always an honor, Stay Blessed Danner Family🙏🏻🙏🏻🙏🏻

[@Pablo_Automotive]

Thank you so much Paul

[@raymundsantos2324]

Thank you Mr. Danner! -from the Philippines

[@Theguv-nor]

Great video as always.

[@markjohnson-fd3qs]

Thank you for both videos. It cleared some things up for me.

[@ScannerDanner]

Glad it was helpful!

[@blakestone8088]

You have isolated the component in question This is where I would Continuity test across the horn input leads No Continuity means - Blown Open Coil "No Need to Go any Farther" (The Harder it has to work the more power it needs to do the work, It Becomes Exponential) That much draw comes with that much heat Heat and Current find the weakest Point & Pop, you're out of commission But You're Teaching Voltage Drops... In the vehicle it would be part of a system There you would be best measuring Voltage draw in action Good Show Thx Paul Side Note My New Fuel pump that's not pumping, did not prime using external pump, or vacuum pump Tanks coming out! After some rest and healing, I'm ready to do it Again lol

[@blakestone8088]

update We're up n running

[@ScannerDanner]

What did you find?

[@blakestone8088]

@@ScannerDanner Pulled it, tested functionality in a cup of gas - Tested Okay (Pump Works, that's not the problem) The pump filter was flat on the bottom of the tank, I rotated it up, put it back in after readjusted the filter screen Added Power to the contacts pump put 40 lbs onto the pressure gauge - Tested Okay Vehicle Starts & Runs Conclusion: (I'd say the screen sitting against the tank bottom, eliminated it's ability to draw gas into itself ("Plugged it") I'm Taking Er Off the Blocks The Worst Job is Now Done! "Next!" lol thx Paul

[@matthewazzopardi5369]

I still love your videos Paul keep up the great content

[@martinhansen8346]

Always interesting content! Keep it up

[@coryhinojosa8020]

Awesome! Info Paul aka Scanner Danner!

[@손정민-v8k]

Awesome Outstanding job thanks

[@onemechca]

As usual, great explanation Paul. Thanks bud. 👍👍

[@ThunderbirdRocket]

Extraordinary detail ! Super helpful !! I learned lots !!! Thanks mate . 👊🏼 🔥 ⚡️ 🕊

[@natepeterson7145]

I had a lesson in AC voltage on a heater. All my safeties tested good on resistance but no heat from 240 vac heater. Rigged up test live and tested each side of the safeties and on one I was getting 240 vac which told me the safety I was testing was bad because I was getting 120 volts from l1 and 120 volts on l2 that went through the heater to my safety. Now I get the phrase electricity follows the path of least resistance because if the safety was good then the heater would've gotten the 240 volts instead of the safety.

[@ScannerDanner]

AC voltage troubleshooting is so weird to me at times lol. My electrical buddy says the same thing to me with the 12v DC systems

[@natepeterson7145]

@@ScannerDanner for real especially when you get 34 volts on a neutral wire.

[@charlesshort4287]

The test light is connected to ground that's why it will light up when you hit the power side hook up, And it won't light up when you touch it to the ground side hook up, Because that would be ground to ground, Good video I understand, And when you 1st hooked the pump up And giving it 12 volt power, The pump should have worked, You will never get the test light to light up Touching ground to ground,

[@ScannerDanner]

Yes you will! Watch part 1. If the ground is open and the motor is good your test light will light on the ground wire

[@Mako-sz4qr]

Thanks man 👍🏻

[@oneilwilliams653]

Excellent work,teacher

[@kevinedward1234]

Paul, Caleb great video!!!!

[@richardmitchell7836]

That poor horse, The " pro's must have been out in full force. IMO I like the data that you instill in my noodle!

[@SeanBZA]

Horn quick test when connected like that is hit the back with a big spanner. Most likely it will make some sort of noise for a while, fixing the worn internal contact. Same for a failing fuel pump, a bit of percussive maintenance will get it to run possibly, till those brushes fully fail, or the commutator finally burns out.

[@amarabdelli487]

Wonderful video thanks

[@SkillSavvyDIY]

Shows how to diagnose properly then shows his Jeep on fire haha, just joking, I've been following you for a long time and you definitely know your stuff. I enjoy the videos and thanks for sharing your knowledge.

[@ScannerDanner]

Man, that jeep....I'm still shaking my head. All that was done was a student did the valve cover gasket BUT, I blew chunks of heavy carbon out of the top of that engine to clear out the drain back holes (300k with crap oil change maintenance) My theory. A chunk of that carbon landed on the exhaust manifold and didn't catch fire until I stopped to get coffee. It then lit and burned right below the main harness and fuel rail.

[@accaautodiagnostics]

Thanks!

[@jeffco908]

Thats where a test light with a built in volt meter works great and they are not expensive at all. Snap on eect400 is what i use.

[@JamesSalcedo-if7bo]

I also use Load Pro leads on a DVM, you can load the circuit with 500 ohms and confirm and resistance of the wiring is ok on both sides before the pump/horn etc.

[@ScannerDanner]

To each his own. I'll just use my test light for that same senario

[@SALTYSPITOONMOTORS]

I get myself confused watching this guy do things I already know how to do correctly...I already learned so much off him I keep expecting to find out I've been wrong for years lol

[@ScannerDanner]

I'm sorry, what were you confused about? Thanks!

[@SALTYSPITOONMOTORS]

@ScannerDanner oh nothing man I'm just joking around. You just taught me so much already that when I see you talk about something simple like this one I just expect to find out something I thought I knew for sure is actually wrong and I'm screwing up my diags lol. Thanks for your work man found you through your forum when I was looking for answers on a nightmare VW electrical diag years ago been subscribed since

[@ScannerDanner]

​@SALTYSPITOONMOTORS my man! Awesome, thank you!

[@pfsantos007]

Posting this in my 5 favorite car diagnostics channels in the faint hope someone will pick it up. I'm just a DIY'er that doesn't want to waste money on the parts cannon. 2013 Mercedes E350 with the M276 3.5L V6 - only way I can afford this car is because I do the work myself and stay away from the dealer. Two codes, P2177 and P2179. System Too Lean Off Idle Bank 1 and 2. Long term fuel trims are ~ +40 Bank 1, +30 Bank 2. Fuel trims stay up at idle (+30, +20 roughly), but not as much as when driving. Short terms trims are up 5-10% when driving, then negative 5-10 when decelerating and then stabilize to 0 at idle. No vacuum leaks at idle - 21 inHg at idle. Changed intake seals (green upper, red lower) and MAF sensor because it was cheap - no change. Car drives perfectly fine, no misfires. Pulled oil cap off, no significant vacuum holding it shut. But if I open a propane bottle into the oil cap hole or dipstick, the fuel trims go down, but not sure if that's normal as the PCV system would suck those fumes, no? I know + fuel trims mean too much air, or not enough fuel. But if it was a fuel issue, wouldn't the problems become worse at a higher load? Because car accelerates fine and has good power. No misfires. Also, capped off the EVAP system and brake booster - no change (at idle at least). No other codes, just the two. Scanner shows MAP, Load, Fuel Pressure all responding normally. I’m lost.

[@АлексейДовженко-ю5ъ]

Thanks to Paul for some great testing of indicator lights. Now I'm looking through your playlists on KZbin, chapters 17,18,19. The first videos in the playlist were filmed 10-11 years ago, you have a pilot lamp in the shape of a screwdriver, it would be interesting to know how long it worked for you, and are there pilot lamps on sale now in 🇺🇲? I recently saw such a lamp on a Chinese 🇨🇳 website. Oooh, this is the lamp that S⚡D had Thank you very much for sharing tutorial videos on KZbin 👨🏼‍🔧....

[@ScannerDanner]

We are working on an SD test light as we speak! I'll announce it when it's ready

[@smid2550]

Excellent work, and if you think about the wiring/motor scenario - a motor goes bad from use, so how could a motor go bad and fail if you had a wiring issue at the same time?

[@karolisgarbaciauskas5445]

Nice👍

[@WrenchsAndAnime]

Great video, I was wondering if you could make a similar video showing how to use your test light to power something on. I’ve seen you do it multiple times but still not 100% on how you know when it’s going to activate the component your testing.

[@ScannerDanner]

Current flow of the circuit and the light must be known. A relay coil draws about 100ma, my test light draws 200ma. The test light will energize that relay coil! Make sense?

[@WrenchsAndAnime]

Thank you

[@bernardocisneros4402]

You gotta put the blame on the mechanic for that Jeep going up in flames🤣

[@ScannerDanner]

For sure!

[@benoitbessette658]

i use a load pro. the best of both worlds

[@barryhoneycutt3894]

Like the channel - subbed from SE Texas Bear ❤💯🙏

[@bernardocisneros4402]

Is it true that Texans love licking longhorn nuts.

[@wichomolina6261]

Podrá acer videos en español.. gracias como quiera aprendo mucho bendiciones ❤

[@dxxxm231]

I had a broken wire going to oil control valve on Hyundai. Fixed the wires and then the vehicle would start and stall. The oil control valve was stuck on as well. Should have played the lottery that day.

[@ScannerDanner]

That makes sense. The oil control valve hadn't moved in how long with the wiring issue. Fix the wires, the valve moves for the first time in forever and then sticks! 🙂

[@adamapsitis6325]

Both methods have their merits; a DMM provides a more qualitative measure, whereas the test light provides some load. I wouldn't like to say which method is "Best" as always it pertains to the circuit in question. What's probability more important is knowing your circuit design and the limitations/variables of any tests you plan on making. More importantly as Paul said, testing under load is vital and the consumer provides that "Load." I used to test with various load test lights before i properly understood Voltage drop, but hardly ever do so these days. A more advanced progression of your diagnostic skills, is to understand the "Most likely" the root cause of failure, and not get caught up with obscure possibilities that almost never occur. I struggle/d with this for the longest time, and tend to always keep myself in check by asking myself the most likely root cause and parking anything else untill necessary.

[@ScannerDanner]

Thanks for this comment. Couldn't agree more

[@georgebell3964]

👍

[@98audiquattro]

Great video, just wondering is it safe to use a test light on 5v sensor circuit to check for voltage drop?

[@ScannerDanner]

Use a voltmeter. There is really no need to use a test light to test a 5v ref circuit. In some circumstances you can, but you need to know what you are doing and most certainly know the current draw of your test light

[@JamieLee606]

I've been in a nightmare trying to help a friend on their 2008 gmc 1500 5.3. DTC showing no communication with TCM, no oil pressure reading at gauge, windows acting up. Testing at DLC, have 60 ohms on pins 6 and 14, Testing low speed bus splice pack under the dash, I'm averaging around 4.5v but every few seconds 11.2v is spiking for split second. It shows up as soon as the key is in accesory, plus run. It only happens on pin M once all other pins are isolated. Pin M goes to the BCM. Only way I've gotten it to go away is either pulling the DLIS 2 amp fuse, unplugging the ignition switch, or unplugging the X1 connector at the BCM. We've cleaned almost all grounds and checked most power connections. We've unplugged just about every module on low speed can bus, the spike stays on until the BCM goes to sleep. It almost seems like there's something going wrong inside the BCM circuit board. It spikes 11.2v every 3 to 5 seconds, then bk to 4.5v. Its been a nightmare lol.

[@ScannerDanner]

What is the voltage range of the low speed bus you are testing? Is it a single or two wire bus? You really need a labscope to look at network signals. Relying on an average voltmeter reading is difficult

[@andrew7202]

I also feel like they both work as long as you understand the fundamentals of this test. But it’s more about people one guy is a numbers guy and one guy is just seeing if it works. I’m the numbers guy lol

[@rksg2003]

Paul was this an infomercial for otc test lights? lol

[@ScannerDanner]

Lol right?

[@JamesSmith-xs7sr]

A faulty component, (starter etc) can show (for example) 2.4 volts drop cranking could be a starter? If you know the cables ate good?

[@ScannerDanner]

Amperage measurement would answer that 2.4v drop

[@SPMech1]

👍👍👍👍👍👍👍👍👍👍👍👍👍👍

[@kenmelrose3429]

" Wolves at the Gate " is an Christian metalcore band

[@ScannerDanner]

Yes sir

[@ralfsautomotive]

Have you tried the load pro on a meter?

[@ScannerDanner]

Never felt the need to own that tool. In part because the owner liked to bash me publicly lol. Good tool, has its place, just not in my arsenal

[@ceciliasalamanca9102]

HELP! So my truck is 1999 Dodge Ram gas and I have "no bus". I have been watching your videos. So I did the 5v test on map, crankshaft, tps but couldn't locate camshaft sensor. So with the ecm connected and key on i get 2.47v on all of them, then i disconnect c1 from ecm the volts went up to 3.58 on each of them, then i disconnect the c2 from emc and volts went up to 5v. So does that mean my ecm is bad?

[@ScannerDanner]

Nope, sounds like a short in the ref circuit itself or one of the sensors is pulling it down. One one 5v regulator on your 99, not multiples like newer cars. Your computer is not the problem

[@ceciliasalamanca9102]

Thanks! I was really close to ordering an ecm. I'll keep searching.

[@danielschmidt2721]

I’ve seen a bad component and wiring issues “burned pins”

[@ScannerDanner]

That's different. Burnt pins on a failed component is not wiring issues up further in a harness

[@danielschmidt2721]

In most cases yes 99% of the time it’s either a bad component or wiring and I 100% agree with you. What I mean is I’ve had plugged cabin filters cause a blower motor cause higher amperage and cause burned pins causing the wire insulation to be brittle and cause a short to frame so replacing the failing blower motor will not completely fix the issue but the wire repair is needed too. But again I always appreciate your content, it’s always a great learning experience.

[@happygarage6310]

When the output is static, it's just a wire. For all those who would bust out the scope for this, you're wasting time. A scope is a good tool, but it is unnecessary for simple testing.

[@bernardocisneros4402]

What's up with all the female bots leaving comments? You know most of these women (probably men) aren't interested in videos like this. Even some of their comments don't make sense or relate to the video. I haven't seen this on other KZbin videos.

[@ScannerDanner]

It's been every new video lately! I've been banning and reporting every one of them. They should be gone now smh. Thanks for the heads up!

[@tonysantamaria19]

So, maybe I missed it, but how does the meter show 12 volts at ground (17 minutes in) when the ground wire is open? Don't you need the positive side and the ground side to light it up? Ground to ground should not make it illuminate. Shouldn't that be a short? Where am I wrong?

[@bernardocisneros4402]

He's trying to show what happens when checking an energized circuit with an open ground. The electricity flows through the resistor, then through one of the wires of the little motor into the little motor, but since the other wire from the little motor is not connected to ground, the motor doesn't run because the circuit is still open (not complete). You should read a book or watch some videos on basic electricity before watching videos similar to this. If you don't, it's going to confuse you and hinder your learning. Even better, grab a couple of light bulbs, some wires, a battery, and a voltmeter. Connect them in series and check them with test light and voltmeter. Then connect them in parallel and check with light and voltmeter. Check before and after every light and make note of the light and meter readings. This is basic. It's like adding 2 plus 2 in math and I'm not exagerating.

[@wayneschirmeriii6487]

You are not wrong that a short to power on the ground side of a basic motor circuit could also cause the test light to illuminate. The next step would be to unplug the load (horn) and retest the ground circuit on the vehicle harness side. If the test light still illuminates, or meter still measures voltage on the ground circuit then this suggests a short to power condition on the ground circuit to the motor. A common cause for this that I have found is a bent pin in a harness connection. The ground circuit pin bent and touching a nearby power circuit pin. A less common condition than a failed horn or motor but still a valid question you presented.

[@bernardocisneros4402]

@@wayneschirmeriii6487 A short to power on the ground side of one circuit is a short to ground on another circuit. This is not what Paul is showing at around 17 minutes of the video and that's what the question was. Paul is showing an open ground.

[@brycelund4112]

Since there is not a complete circuit. You will measure the voltage through the load. That’s why the meter reads 12V with an open ground. If the circuit was operating correctly. The meter would read close to zero which would indicate a good ground.

[@ScannerDanner]

No current flow, equals no voltage drop. Power comes into the positive side of that motor and comes out the negative side "looking for a ground". A voltmeter will show 12v (same as the source) regardless of the resistance of the output. Let's compare 1 ohm (electric motor) to 150 ohms (relay coil) for this example. Both circuits will show the same 12v with an open ground when using a voltmeter (no current flow, no voltage drop). Now, let's use my test light. Remember that connecting this light, in this way, with an open ground, is basically putting another resistor in series after the load. The 1ohm circuit will have very little drop in voltage, so my test light will be very bright. The 150ohm circuit will have a large drop in voltage and my light will be very dim. There are variables within this test too, and one of them is my test light itself! The light I'm using draws about 200ma. To put this another way. The motor I'm testing probably carries 3-4 amps and my test light can only carry 200ma, that is why the ground wire is so bright. If this was a relay coil that draws less than 100ma, my test light would have no problem energizing that circuit (at least partially anyway) and the bulb would be very dim in that test as most of the voltage dropped across the first resistor. Lol. Now I'm rambling. Lastly, you will never troubleshoot a short to power on a ground wire. Why? Because you would attack that problem as a short to ground on a blown fuse or possibly a blown out computer driver on a power side switched circuit. But even with that, you're testing the power feed wire for a short to ground. Never the other way around. At least in your head anyway.

[@ljchrzan]

Can you wack that horn and make it work?

[@ScannerDanner]

I believe I tried in part 1

[@throttlebottle5906]

it would have been very funny if the horn suddenly started blowing at 7:00 when banging hand around it causing vibration. yeah, they sometimes start working again short term when banged around. no need to ask how I know (the knots on my head coincided, with head hitting it on the hood)