Helping Auto Tech Student Pass Basic Electrical Exam

A local automotive tech school student requested a video to help pass an electrical exam for class. We cover test questions for electrical definitions, wiring diagrams, voltage drop testing and do live applications on a car using multimeter, test light and oscilloscope as required for the test. This might also be useful if studying for an ASE test as well.
Visit my website at www.schrodingersboxQM.com for more training videos and great case studies!

[@keisha5425]

Hey! Young female tech apprentice trying to teach herself something commenting on your channel again! I might have to start watching your newer videos haha! This felt like a full on college class I would have to pay for! Very impressed with the progression from your older videos haha! I'm in the middle of trouble shooting an intermittent no crank on my mom's old truck, just trying to help her out a bit while learning something. Rewatching this video a hundred times, a fair amount of banging my head on walls, and getting my damn money's worth out of my DVOM, I'm almost certain I have a bad Inhibitor Relay or problems with the wiring to/from it. I'll figure it out for sure tomorrow haha. But I'm certain if I hadn't come across this channel I probably wouldn't have even tried to figure it out! Going over the water analogy helped me so much! I understood the concept of resistance but was a bit confused on the amperage and voltage, you cleared that right up for me! And that voltage drop test explanation was absolutely invaluable!! I don't have heaps of money but at this point I have to get something from your shop to support the channel. Thank you Mr. Matt I really appreciate the effort you put into your videos! :)

[@SchrodingersBox]

Hi Keisha yes I remember you from a while back. Thanks for the great comment and glad to have helped you explained you ability. Incidentally, the student who contacted me is a female!!

[@rajkamalaarya75]

It's afternoon here.. Love from india 🇮🇳

[@SchrodingersBox]

Hahahah all my internationals are skipping work to watch a video it seems!!!!

[@sharvaaharen3243]

Hey Matt, out of my campus your lecturing videos are treasures for me, I am doing motive power technology, Centennial college Canada.I am your paid content subscriber. Those videos and pdf book are my study materials, i am about to graduate, as well as i recommended your website and you tube links to my juniors and most of my lecturers.

[@SchrodingersBox]

great to hear and “congraduations” as i like to say!!!

[@daveberger4675]

Good presentation. Reminds me of the fuel trim video/s.

[@pocitpubg]

This is insane video I love it thank you for sharing your knowledge with us. Big fan bro

[@SchrodingersBox]

I appreciate that!

[@HouseCallAutoRepair]

Matt... Lovin the refresher course! One potential issue... I THINK that using the test light to demonstrate voltage drop, they possibly meant measure voltage between source voltage (A) and point (B) and with the volt meter still connected, connect test light to (A) and (B) to show how the test light pulls it down. The paper clip trick can also get you in trouble in "integrity self check" circuits. You'll get a "circuit shorted to B+" errors stored in the PCM/modules.

[@HouseCallAutoRepair]

I forget to qualify the circuit being tested for voltage drop Difference between (A) and (B) MUST be a loaded circuit, else no current. The test light would provide additional load on the circuit, thus and more noticeable voltage drop. Missing a detail can completely change the context. Sorry Mat t I forgot to include a very important part

[@henryriley9955]

thank you! Automotive student from Michigan! Appreciate what you do!!

[@SchrodingersBox]

Glad to hear!! Yes I always appreciate automotive techs and students on the channel!!

[@henryriley9955]

Im currently in level 1 electrical, so this is literally summarizing the entire course into an hour. This is absolutely perfect and helped me understand available voltage, voltage drop, and finding voltage loss.@@SchrodingersBox Just the scientific aspect of it makes it super friendly, so thank you!!

[@tonycastro6154]

hahaha been doing auto electric since 1984,,this questions are so freakin confusing, like when i use to get electronic college courses,,,when hands on,,all is so easy to learn,,,we need more apprenticeship availabilities', in the end no title matters only to snobs, its the hand on experience that counts,,,in my view,,,old school thought,,,

[@tysonrinker5958]

I agree but studying and taking the ase tests have taught me so much

[@punditgi]

Excellent video! 🎉😊

[@jamessmith2214]

You gotta know how the system work for sure!

[@DylanL69]

You can do the same side voltage drop on the positive side

[@SchrodingersBox]

indeed. that’s actually where I found the missing 1V.

[@siksclass]

Matt, thank you for your videos. Been a paid subscriber for a year or more. I’m trying to help my mother with her 2013 Lexus es350. The car blew the main use because OReilly’s sold my dad the wrong battery. I got the car back up and running but the brake lights and fog lights are the two remaining things not working. I gave the brake lights direct power with multimeter and they worked so I threw a new brake light switch in and that didn’t solve the problem for the brake lights. So I took to dealer. And they were trying to charge over $900 to change the integrated relay and wouldn’t guarantee that would fix it. “Starting point” is what they called it. If I was going to play parts roulette I could change that relay myself. I already took apart the fuse box and replaced the blown fusible link, and several fuses. I’ve checked all fuses related to the issue and seem fine. So I bought the relay module for $200 from Toyota and still the same. I’m going to give the brake lights direct power again to see if they lit up like before I took to dealer and see if I’m at the same spot. I wish I had your direct line. I know it’s impossible but please send positive thoughts my way. I’m trying my best and you’ve been a great help.

[@SchrodingersBox]

Well I don’t believe in thoughts and prayers but I can provide you a wiring diagram perhaps if you email me!

[@wedo5855]

Amazing character and material ❤

[@crosspoint6870]

Hi!! I have been watching your videos non stop and it opened a world for me man, troubleshooting is my passion! Anyway, I have been diagnosing my roommates car for a few days now and it comes down to this: P0171 Freeze frame: 800rpm 0% load 25% ltft 0% stft Now I hooked up the car to a scanner and tried to see what was going on. I managed to witness the car turning to closed loop BEFORE o2 sensor data. o2 is still at 0v while the car is (as far as i know) trying to compensate for the “fake” lean (0v) condition by slowly raising stft to 25% where it resets to 0 and gives a open loop fault for a second. This repeats about 5 or 6 times until the o2 sensor finally starts reporting good normal data and causes trims to normal. The annoying thing is that its intermittend, sometimes o2 works directly but on most cold starts it doesnt. Even when driving it sometimes reports 0v and gives open loop fault with stft slowly going to 25 and resetting to 0. I thought “good” o2 sensor data was the requirement for closed loop operation?? Im so confused

[@crosspoint6870]

When disconnecting the o2 sensor i get stable 0.3v that the service manual says it should be. I really dont want to be the “just get a new o2 sensor” guy so if you could point me to some possible causes, it would be very much appreciated 🤠 im breaking my head rn

[@crosspoint6870]

And as far as I can tell the car idles and drives normal

[@SchrodingersBox]

Pretty simple- you just need to curve the O2 voltage and fuel trims with engine load. It will tell you exactly where the issue is.

[@crosspoint6870]

@@SchrodingersBox well 9/10 it reports good normal data but ecasionally it stays dead flat at 0v for a while before switching beteween rich and lean

[@crosspoint6870]

I just wanted to know what could be the reason for the o2 sensor to report GOOD data most of the time but sometimes no data at the same rpm’s/load, even after having driven and the sensor being heated up. Its not that its reporting a lean condition its just flat 0v

[@embreesmith7613]

Are those Gladiator vs wall boxes any good ?? I purchased some, but never got to use them. ,🙄

[@SchrodingersBox]

YES!!! They are awesome!! Now keep in mind there are two types of them. You want to get the better quality ones. Absolutely worth it.

[@tonydandrea6574]

i noticed on your drawings you didn't connect the battery minus to ground, hence no current flow.

[@dkupy100]

In a former life, Matt was a commercial artist........and homeless.

[@SchrodingersBox]

actually one of those was true….

[@bernardaflores1720]

nicely done

[@sheerwillsurvival2064]

Your going to be one of those guys in the nursing home. Yelling out equations and solutions and making car sounds in your wheelchair. I’ll be the guy behind ya saying that’s my pole position move over

[@SchrodingersBox]

Hahahahaha - wheelchair races in the halls baby!!!!!!

[@sheerwillsurvival2064]

@@SchrodingersBox you got your on 😁

[@GraditelMacedonia]

That so-called DVM is actually MULTIMETER or DMM! because isn't measuring only VOLTS!? Right?

[@SchrodingersBox]

It’s measuring volts and ohms. Digitally.

[@GraditelMacedonia]

@@SchrodingersBox Very true.

[@stephennichols586]

Depending on the meter most automotive meters were used for just volts and ohms until they started using electronics and the ones I have been using working in the commercial air-conditioning and refrigeration industry have at least 30 different settings now that is a multi meter

[@geraldelwood9660]

Hi, I must say that I think this is a great channel and I very much like your ethos. This is why I hesitate to criticise, but I feel your use of a tap/faucet as your pressure/voltage source is a bit confusing. Personally I would use an constantly full bucket with a pipe coming out of the base. The pipe would be connected to a second similar bucket. The difference in height between the 2 buckets gives us our Voltage / Pressure.. My second point follows on and this is that the important image of Voltage is P.D. Potential Difference. A single point of voltage is of no significance until it has an electrical path to a second point which has a different voltage and the "Pressure" is the difference in potential/voltage between the 2 points (the difference in height of the 2 buckets.) If the 2 ends of a circuit are both at 1000 volts (compared to earth) no current will flow in this circuit. Your image of an open tap with a pipe with no constriction shows full flow of water but you indicate there is zero volts at the tap. Obviously if voltage were truly zero compared to open end of pipe there would be zero flow of water/coulombs. It might also be worth explaining to the students that even copper wire has a resistance which will create a minor voltage drop. This can be very important because this volt drop is directly proportional to the current flowing in the circuit, which is why cable sizing is so important for high current circuits (as the greater the c.s.a. the lower the resistance - the lower the volt drop) I hope this is constructive and I wish you and all the students the best of luck.

[@SchrodingersBox]

In my example the voltage is prior to the tap. Street pressure. Like in an actual water system. There is only pressure at the tap itself when it’s restricted or closed.

[@michaels3429]

I going to watch and rewatch and rewatch this video also probably take some notes lol, thank you so much

[@SchrodingersBox]

That’s exactly how I have to learn things, believe it or not. I have to see it maybe 3 or even 5 times before it sinks in. That’s the truth!! Also to really learn it you have to do it!! Get a DVOM and actually measure a voltage drop. This is the only way to truly learn it. You will only absorb so much from a video.

[@andrejbalog4915]

Michael, then once you have feeling you understand, go ahead and explain it to someone without appropriate background. If you succeed, then you can be sure you've understood. It works for everything!!!

[@SchrodingersBox]

That’s a pretty good measure to follow, in general. I heard it as “if you can’t explain it to a 12yr old, you don’t really know it” lol.

[@rexisretro]

timing too perfect😂 we just starting learning automotive electrical at my apprenticeship

[@tubetime39]

rexistretro; There's a reason for that. Take advantage ,of it (and Matt's videos) focus and hang in there.Keep the fire alive. Good techs needed out there !

[@rexisretro]

@@tubetime39 Indeed🫡

[@rexisretro]

@@tubetime39 I will push myself to be the best tech i can be

[@mintech1000]

Thank you

[@76089randy]

This was amazing thank you

[@SchrodingersBox]

Glad you enjoyed it!

[@name9287]

So cool of you to help out with this🌝

[@SchrodingersBox]

It actually is pretty good premise for a video- actual real life application for students!!

[@name9287]

@@SchrodingersBox , agree...any trouble areas students mention could be useful to other students

[@johnmwangi6291]

Enjoying from Kenya....

[@SchrodingersBox]

Hey my friend good to see you!!

[@stspringer2003]

I posted a comment and I don't see it. It was about the drawing on the relay

[@SchrodingersBox]

what was your comment?

[@stspringer2003]

@@SchrodingersBox It looked to me like the China diagram on the relay was incorrect, it shows the electromagnet in a position that would be pulling the armature away from pin 87, see time-line 1:32:26 The armature would be pulled toward the relay coil which is away from pin 87. It should have the coil on the other side of the armature so it gets pulled to pin 87, or am I nuts? LOL

[@SchrodingersBox]

The diagram is correct.

[@danieljurgill1681]

The initial explanation of voltage and flow using the water hose needs fixed. Make it simple. Here is all you need. If a person kinks the hose partially ,it is 12 volts on one side and zero on the other. If you make another identical partial kink in the hose down stream, it is 12volts, dropping to 6 volts then dropping to zero volts. You went way off base and made it more confusing by using 11 volts, 3 volts, 9 volts etc. In your example you introduced 2 resistors ( partial kinks) with different sized kinks.

[@SchrodingersBox]

But that description would be inaccurate. There is some dichotomy between electrical and fluidics.

[@danieljurgill1681]

@@SchrodingersBox OK, how about 12 psi and 0 psi. Or 12 feet of water pressure ,and 0 feet of water pressure. I am sure you understand . You do an amazing job, talking on camera as you go. Forget I mentioned it.

[@SchrodingersBox]

No. It’s inaccurate that you have full pressure ahead of a restriction in fluidics. Doesn’t happen that way. Electrical- yes, fluidics, no.

[@danieljurgill1681]

@@SchrodingersBox The voltage drop along a wire when current flows is similar to the pressure drop along a length of pipe when water flows . For your simple illustration and explanation you can disregard the small drop in the wire or for water on the pipe. The voltage , is also called potential, potential energy , just as feet of water is potential energy. The only significant difference between electric current and water current is that electric current stops when there is an open wire, where water current stops when a valve is shut. The flow measurement in piping is done through the measurement difference in head in the upstream vs the downstream side of a venturi meter. We used to use mercury manometers on the pump test facility. Every static head measure had to also include the velocity head . But for low velocity flow rates the velocity head was a insignificant portion of the total energy.

[@hindflight]

A 1 volt voltage drop on a 12.6 volt circuit is only about 8% which would be hard to assess with just a test light!!

[@SchrodingersBox]

Exactly!!!!! I am kind of wondering why that’s even a method that would be shown. Maybe I misunderstood the question but I wouldn’t check for voltage drop with a testlight unless it was like a no-crank no start or something where it would be a really significant voltage drop. Even then I still use a DVOm tho.

[@hindflight]

@@SchrodingersBox Agreed, the way the question is written I interpret it the same. Would use only DVOm for this myself. Especially since a 20% to 30% drop could be sufficient to affect a starter motor, but maybe hard to detect with a test light. Great video as always Matt!!

[@JuanVargas-tl5dj]

Good video bro

[@SchrodingersBox]

Thanks for watching!!

[@stephennichols586]

Th6 higher the voltage the lower t6 amperage l0wer voltage higher amperage

[@asonofgod_98]

Hey Matt, yesterday I diagnosed a battery drain on a Nissan Sunny ex saloon and we left the battery connected overnight and this morning she started. I learned that from your videos you did long back. I used the method of checking m-volts on each fuse instead of pulling the fuses out one by one, and it worked. Now that customer of mine has got a friend of his that’s got the same problem, and automatically I’m the one that will fix it 😂. Good stuff, I’m learning a lot from this channel. Brighton from Zimbabwe 🇿🇼, bye bye 👋🏾.

[@SchrodingersBox]

Great story!! Congratulations!

[@moba2k]

This is hands down the best video I’ve found on tying theoretical and conceptual electric knowledge to hands on application - a system we use everyday, a car. Helpful for test taker and also the rest of us. Thankful for Schrödingers box and KZbin. KZbin POWER !!!!! DIYers unite and build shit!! YEEEEAAAAHHHH!!! BTW I like imagining a fuse blowing 💥 as a bridge collapsing causing traffic (or any kind of flow) to stop. Thanks

[@embreesmith7613]

Bernie !! This just showed up in my feed today Hello to Ms Vikki and the Cat ya old scror. 😀😀😀

[@allanfranco4464]

AWESOME EXPLAINATION AND TEACHING I GOT IT THANK YOU SO MUCH FOR SHARING YOUR TIME AND KNOWLEDGE

[@asonofgod_98]

I’m the first one to comment 😅. Brighton from Zimbabwe 🇿🇼 here.

[@SchrodingersBox]

hahahahaha. well not fair when you are in a time zone 12 hours away lol!!!!

[@asonofgod_98]

@@SchrodingersBox 😂 its 09:57 am.

[@nickayivor8432]

👍 PRODIGY Schrodingers Box From Nick Ayivor from London England UK 🇬🇧 ⏰️ 11:51am

[@scottpollard3270]

Sorry to hear about your paperclip. I completely understand.

[@SchrodingersBox]

Finally!!!! No one seemed to care!!! Until now :-)

[@Mark_C1]

We understand bud. Be it a trusted paper clip or snap-on ratchet we feel that same pain 😂

[@SchrodingersBox]

I’m just glad I didn’t lose my $50 snap-on paper clip!!

[@oliversamson2231]

This is great, i learn a lot, thank you very much, anticipating for more ❤❤

[@SchrodingersBox]

Glad to hear. There are also hundreds of hours of videos like this on my website as well. Www.schrodingersboxQM.com.

[@JasenFromBoston]

v.a.r. volts amps and resistance where to find one you use the other 2 so v=a / r or r= a x r etc.. easiest way to remember it

[@stephennichols586]

SP St single pole single throw meaning you have a common terminal and a NO normally open and a NC normally closed terminal and it can be a DPDT double pole double throw meaning two independent switches ones could be normally open or both or one closed and one normally open

[@carlosvilleda284]

That knowledge is well appreciated

[@davidcoudriet8439]

Angry cat t- shirts!

[@stephennichols586]

To determine what is causing the voltage drop wouldn't you check the voltage at the light switch relay and before and after Ny connectors you could replace the positive wire and then still have the voltage drop because of the light sw

[@SchrodingersBox]

Yes exactly correct. It’s possible- well, actually likely that the voltage drop is between relay and bulb. Also I need to check at the other bulb to see if there is voltage drop there too.

[@Elchin206]

You are the best. Thank you at all.

[@balkee42]

Hey man i posted this question on another vid but in case u dont see it : i found like a yellow paste in my radiator hose on my acura tl. Would that likely mean a blown head gasket?

[@SchrodingersBox]

Could be. Whats your compression pressure?

[@balkee42]

@@SchrodingersBox for cooling system? Ive not done it yet ive got a lot off the car doing maintenance. In process of getting everything back on so i can crank it. So the cooling system compression test would tell me for sure?

[@SchrodingersBox]

You want to do cylinder compression.

[@nathannangle6354]

So to summarise the voltage drop point, if you measure before the load by putting the positive lead before any load on its power wire, wheather it be a light bulb, a wiper motor feed, a fuel pump feed, and the negative wire on the battery ground, or body ground, you will measure 12 volts dc. If you them put the negative lead on the return wire from the load, like the black wire from your light bulb, or the negative wire on a fuel pump or wiper motor when turned on, you also read 12vdc but this is the total drop across the load, so healthy circuit. If you measured only 8 volts across the bulb, you have voltage drop, so you check the bulb connection or element, or the ground wire for a large impedance, or resistance, and once found and fixed the voltage drop reading across the load should be 12vdc once more to indicate a healthy circuit.

[@SchrodingersBox]

Correct. Just one addition in your last paragraph- if you didn’t find the 4 volt drop on the ground you would also check the power. In fact as you saw on my own car my power side has 1V of drop, almost none on the ground.

[@nathannangle6354]

Thank you sir, Regards from County Meath in Ireland

[@robertjospeh1097]

Are you sure the test was not for can high and can low.

[@SchrodingersBox]

Yeah I am sure. It’s clear low and high side refers to ground or power control plus it specifically mentioned of a driver. That’s a transistor.

[@robertjospeh1097]

Thank you@@SchrodingersBox