Hi Matt. I'm retired now after 42 years as a mechanic. I worked on heavy trucks then switched to elevators. Dealt with relay logic elevator control circuits for many years. This was spot on like all your videos. THANK YOU for sharing your knowledge with us and for reminding this old mechanic that it's good to be retired : ).

You are one of the best teachers on car electrical circuits on KZfaq. Keep it simple even though the topic is not. At 8:20, you helped me understand relays with more than 4 terminals. Thanks

I don’t see how anyone can dislike this man. Hands down the best automotive YT’r for troubleshooting. Solid content.

Thank you so much for both relay videos. I've been trying to get my head around how relays work for years, and finally the control side (reasoning and understanding side) in my brain activated the load side(common sense side) to allow me to finally "get it" within 5 mins of watching your 1st video

Great diagnostic. You broke down that issue perfectly. Bravo. You said you only have a basic understanding of electrical diagnostics but obviously you don't give yourself enough credit. You are easily on an intermediate to advanced level. If you can diagnose a bad combination switch (light stalk) then you're definitely not a beginner. Beginners don't even know how to use a multimeter to it's fullest potential and you whipped right through voltage and resistance testing. The only thing wrong you did in this series is not properly evaluating your own skill level. You might think you only have a basic understanding but isn't that always the case? Everything seems basic when you know what you are doing. ;)

Absolutely brilliant! 9/10, I start at the relay(if applicable). The main differentiation for your diagnoses you want to make at the relay is this....load side fault or control side fault. That is extremely important and very useful. Every step in diagnostics should point you in a direction and if it happens to be the same direction as previous tests have indicated, you are more than likely headed in the right direction. In a matter of minutes, you can easily erase variables that do not pertain to the condition. To this day, this is one of your best videos Matt, congrats my friend.

thank you again Matt...I spent sufficient time watching your part 1 n 2 relay videos n I am proud to tell u that now I truly understand how relays work..God bless u more...

I have to say, I really enjoy your method of explaining how things work.

Dude, this video is brilliant (along with part one). I understood about 85% of this before hand, but this really connected the dots for me. Thank you!

Question for Matt: My wife's Chrysler T&C 1998 van uses a "solid state" type relay rather than a coil type. Could you do ( or do you have) a vid explaining how this type of relay works? Also, is it possible to test these without special equipment, like anything other than a DVOM? Thanks for this awesome series and keep them coming! WARNING for all viewers of this vid: While Matt's 2 part series on relays is fantastic and honestly, the BEST explanation of relays I've ever seen, PLEASE understand that not ALL headlight circuits (or any relayed circuits) are necessarily this simple. I have a Subaru Forester S, 2001, and both lights failed simultaneously last winter. Fortunately, I found ultra cheap (like 8 bucks) pdf file factory shop manuals on ebay, so I have the actual wiring diagrams for my car. In my car, the HL switch actually closes the ground circuit to BOTH the HL (load) AND the HL relays' control coils. In addition, the POWER side of the relay control coil is switched by the ignition switch (only HOT in "RUN"). Most cars don't require ignition switch to be on to operate HLs, but if you have a Subaru, I almost guarantee yours does. In my situation, you have THREE, not just one, switched locations in the circuit that could have been bad. Diagnosis could be done using Matt's method, but would have been quite a bit more difficult, since even in a working state, you'd have NO continuity to ground or power at rest on EITHER side of the relay control sockets in the fuse box. I respect Matt very much, but in my experience, the 8 dollar shop manual is worth it's weight in gold for the wiring diagrams alone! They've saved me SO much time. Incidentally, the issue turned out to be the ground wire from HL switch connector to the HL connector was burned and part of the connector melted. I got a new connector at the junkyard for ONE dollar. Unfortunately, had to spend 12 bucks on a special tool to get the pins out of the connectors, but still, was a fun repair!

I learn so much from this channel. Thank you for taking the time to make these videos. They are very very good!

I learned so much from your videos that must to watch them a few times so won't miss anything, please keep doing videos!

Another masterpiece. Now I have the confidence to tackle my no brake light problem tomorrow.

Ive been watching all your teachings and I have learn a great deal, thank you so much , I am so seriously wanting to learn more , about how to test and Diagnose all electrical, I know the mechanic all ready .

Very helpful ! I learned lots of new things . You explain things very well ; and the illustrations make the concepts crystal clear !!

I’m continually impressed by your videos. You are also the only other person besides myself to use the term “in lieu of” in normal conversation. One of the guys I work with had to look it up when he read one of my emails. 🤣

Fabulous video! My understanding of relays finally clicked, no pun intended! Thank you so much. Trying to be a 2%.

Learned a lot with this series. Thanks Matt.

nothing like real-life experience to drive a point home ... even though i had watched this video a while back, today i assumed that a clicking relay was a good relay and went on to waste about an hour checking other stuff. finally came back inside, re-watched this video, performed this SIMPLE, EASY, QUICK, DEFINITIVE relay test and determined that although the relay had continuity through the load side when energized, it was not passing current. never again will i think that a clicking relay is a good relay !!! great videos ... good camera work and i love the way you combine the DEBOK with actual cases. keep up the great work !

Muchas gracias! A pesar de ser en ingles los entiendo claramente. Aprecio todo su esfuerzo. Dios lo bendiga desde Venezuela y nunca deje de colocar sus enseñanzas

Thanks!! you have been a great help on helping me learn on troubleshooting electrical problems and solving it.

Thanks Matt for your teaching skills

This was so awesome to find. Explained better than I have ever seen.

Vic here(shade tree ass hat) just want to thank you for sharing your knowledge,you a good man!

These are very informative videos both for the novice and experienced.Even though I have never used a Power Probe, it is a very versatile tool,especially for the novice where it is very easy to do a straight short on the main power lines.As the Probe will cut out in this situation ,it prevents an under hood barbecue.It behaves like the RCD on the house mains.From experience,the main contacts can be closed but due towear and pitting, no real contact is made.

Thank You ! Just signed up to website. Why not at $3.49/mo ! Lots to learn. Have loan ( & ins !! As it sits 12 months now) on 2015 Promaster Van no one wants to work on with wiring issues. Another promaster owner told me dealership (Dodge, Chrysler) told him to come get his they couldn't fix his wiring problems.

Great stuff thank you it is just cemented the information I have been reading I have tackled and eight pin relay which is a lot easier now that I have seen this and tested it. Thank you very much for this helpful video liked and subbed will share with the guys at my shop.

Thx again 4 your time! In this video u essentially worked BACKWARDS electronically (like the old dayz) to find the trouble which eventually was the headlight switch. The process of elimination... although I like yur way better even though it's a bit more complicated.

This is good stuff Matt. You are top shelf.

KNOWLEDGEABLE Schrodingers box Sharing what you know with us Thank you. Tutorial loved it video great from the start to finish 👏 👌 👍 Take care and have a great day Schrodingers Box From Nick Ayivor from London England UK 🇬🇧

Really well done!

great teaching on how a 4 prong relay works thanks

Thanks for your videos,fixed my central locking,didn't need to replace any parts,contacts inside the actuator were rusty.

Great hands on tutorial !!!!!!!!!!!!!

Super videos. Thanks so much!

BRILLIANT GENIUS TEACHER

Just an EXCELLENT explanation....KEEP doing this...

Absolute LEGEND....Thanks....

Awesome video keep them coming!!!

It was definitely helpful,hermano!!!

Wow amazingly helpful , before I watch this video the only knowledge I had of a relay involved switching the Batten from your hand to the next runners hand 😂 now how to find the relay switch responsible for my AC blower , heated seats, reverse light and wing Mirror controls , which all went down together after having to recharge the dead battery on my 2003 Audi TT ... someone mentioned there is no relay for the blower on the TT , then somebody said they found a whole box of relays under the bonnet somewhere , any insight on that would be more then welcome 🙏 , at least I’m not rushing out to buy a blower motor now thanks to your great way of teaching and live examples kindest wishes

Freakin awesome as always!!!

Great lesson! Thanks! I was the 600th LIKE!!! (Love when that happens)

Watched part 1. Boss!

Nice helpful video, thank you so much

HEY!!! Isn't it about time for another mailbox segment? I am in need of a good belly laugh, and the bathrobe and pipe would definitely do it for me. :) And I'm also ready for some more caustic comments towards the people who keep running out of gas so they replace their muffler.......

Awesome information

badass keep goin man

Great video, Informative and educational. Only downside is most of these practices only apply to vehicles up to 2004. After this manufacturers started using CAN networks. Ecu's and modules control lighting directly.

Amazing thank you Schrodingers

Very nice video, while I was watching your vid being a flat rate diag tech I was thinking of your diag steps one step I though you were going to due was just bypass the headlight switch all together since you had the connector in hand and you knew what circuits came in with voltage and what circuit or term was the output of the switch another thing I think is so very important when doing this type electrical diag work is to make sure u load test circuits I use a 9007 headlamp bulb that a that I rigged up i can interchange alligator type clips or pin type term, maybe your next series should be about the importance of load testing circuits and how to do voltage drops factory pin point tests tests for open, shorts to power and shorts to ground but not resistance within circuits.

nice information thx you very much

Tech tips; Here are a few thoughts about relays on cars; Much of the time, the relay will be referred to as the standard "Bosch 5 pin relay" type. It is an industry standard. They are made by many companies, and are easily available anywhere. But the "Bosch style" is not always used. Other types and designs are used as well. But the Bosch style is used on most modern cars. The 5 pins have universal meanings. Each terminal has a specific universal number, whether the relay is labeled or not. The linked articles cover that in detail. The pins are also positioned in a universal way so that you can see which pin does what, by looking at the bottom of the relay (the pins, or blades). In other words, if you memorize (or use a picture of) what each pin is used for, based on it's position and angle, that will be the same on every Bosch style 4 or 5 pin relay. And the numbering is also universal (i.e. Pin 30 is the high amp input, pin 87 is the high amp output, etc.) I THINK, but I am not positive, that the color scheme for all 5 wires is universal. You'd need to research that, but I'm fairly sure that each of the five terminal wires on a proper socket would use the specific colors, but I have also seen reference to sockets being sold that don't have the proper color wires attached to the proper socket hole, so be careful with that. The sockets, with a few inches of pigtail wiring are available at any auto parts store. When replacing a relay, it is important that the relay have equal or greater current ratings as the original. Usually, both the primary and output sides will be rated, for example, something like this: 20/30 It means 20 amps rating on the input coil and 30 amps rating on the output. Of course, having 20 amps on the primary side virtually never happens on cars (it would negate the whole point of using a relay), but the relay does need to be rated to handle the proper output (switched) current. Relays rarely fail. When they do, it is usually because the switching contacts get pitted and corroded, and basically just "wear out". The other typical failure mode would be an open in the coil side (input). Most of the time, when a relay wears out or fails, it is due to the wearing out of the contacts in normal use, OR the output circuit is carrying more current than it is supposed to, which obviously means there is a problem in the switched (output) circuit. The Bosch style relay is cheap, about 3 to 6 dollars. It is important to buy a decent quality one. On many relays there will be a diagram, and it will include the letters NO and NC, meaning Normally Closed and Normally Open. Matt covers that very well. It is not very common for pin 87A to be used. Sometimes it is used, but not a lot. Even so, MANY cars will use a 5 pin Bosch style relay even when only 4 pins are being used. The articles linked below cover that. The input side (the coil) can be power side switched or ground side switched. It will work fine either way, but power side switching is by far the most common. As Emmanuel Munoz mentioned, the coil side can (and should) be tested for resistance. An open on the coil would obviously show infinite resistance. When testing the output side of a relay using a meter or test light, it is very possible for the test to show a good relay, when it really isn't. It only takes a trickle of current for an ohms check across closed contacts, or a small amount of current to power a test light, but the contacts can be so pitted or corroded that they can't handle any significant current, as it is originally designed to. I.E. it might test ok for resistance when closed, or it may power a test light fine, but when used to carry the high current that would be typical (20 amps or so) it just can't do it. So tests for relays can be a little tricky. The purpose of the bypass or "quench" diode that Randy Jones mentioned is covered in some of the links below. But none of them will probably explain it any better than Stuzman does. Many cars use several identical Bosch style (or other types) relays. My car has 4 next to each other in the Power Distribution Box, all with the exact same Chrysler OEM part numbers. So for testing purposes I could switch two of them and see if the suspect one works OK. Some "flasher" circuits (like turn signals) use a connector that will accept a 4 pin or 5 pin Bosch style relay, but don't make the mistake of putting a relay where a flasher belongs. Very, very bad things can happen. Excellent videos, Matt, as always.

I did understand relay operation before this, but now I can actually use the information beyond testing the relay! :) I repeated myself out of excitement. Deleted that. :)

Great review. Very interesting. No pun but, your + appears more like an X on the white board. Best to get the horizontal - flat so it doesn't confuse folks it's an X.

Some comments on Comments (part 1 and part 2): Randy Jones makes an excellent point (video part 1)about the inclusion and importance of the diode on some relays. The resources that I've linked talk about the purpose of the diode. Stuzman52 wrote an EXCELLENT piece (video part 1) about why the diode is there and what it does. Gene Hensley: Most of the links I posted below discuss the usage of the 5 pin relays. Keep in mind, MANY times a 5 pin relay will be installed on a car, but that the 5th terminal is not actually used for anything. But, sometimes the 5th pin IS used. Of course, you'd have to check your wiring diagram to be sure, but when replacing a relay, it is easiest to just get a direct replacement for whatever is already there. Emmanuel Munoz made a good note about testing the coil resistance. That subject (testing a relay) is covered in some of the links below also. Billy R made an excellent point, to use a test light when initially testing the input and outputs of a relay, to limit current.

GM someimes uses a bias voltage I believe on control side of a relay maybe you can explain that to us thank very nice videos part 1 & 2 I learned a lot

Another great video! Here's a question. How would you determine the load side from the control side of a stuck closed unmarked relay. I suppose checking for resistance would be a start? I had a stuck closed relay on a fuel pump that wouldn't shut off. Took an educated guess and swapped the relay with a new one and it fixed the problem. That was when I was a 98%'er

Good video

Hellow Sir, first I want to thank you for your content, very insightful and entertaining. I have a question about a mistery with my car's headlight electrical system. So first of all, I have a 2000 Acura TL that I lost both headlights all of the sudden, both low and high beam. So I checked both fuses and relays, and the bulbs, they are all fine. I have a ect 3000 from power probe, as well as the power probe. Ive traced both harnesses right and left and on the passenger side, there seems to be some kind of ground fault. The right headlight relay show 12v on the control side but no ground, the fuse is also dead, but not blown. when I trace my ground wire im lead to the chasis of the car, than the sound stops when I go passed it. Ive tested all my grounds to the battery, but they are all good, the wireing all seems to be fine but when I try to trace an open circuit, it leads me to the inside of the car, but than it just takes me in a circle. I cant seem to figure for the life of me what could be the issue, any thoughts, Im a DIYer but consider myself to be a decent mechanic and understand automobile electricity pretty good, Im at a loss. What would cause the ground to be absent? I thank you in advance and hopefully you can give me some insight.

Spectacular video. I came here from watching another one of your vids (crank no start isuzu) and now I have a solid understanding of 4 & 5 pin relays. Thank you 🙌... (did you ever work in a shop before by any chance?) Did you ever get your ASE certifications? Just curious as to how you got to your level.. (definitely seems like your up there) 😳

I understand everything you're saying, thank you for this video, one question where are you getting a low voltage from.

Outstanding! You take a potentially complex problem and through a logical plan approach make it so simple. How much $$ did you end up saving that person?

Thanks for teaching and good job. You have done a big thing. Do you have a training class?.

Great video. Wish you had covered a diode protected relay. With a diode protected relay, power has to be applied to the right pin in the load side, right? Usually, pin 86.

OK, I'm on somewhat of a roll here with suggestions............sorry if I'm overdoing it. Although it is not in any way a repair or diagnostic video, I think many of your hardcore viewers would enjoy seeing a video where you do an exhaustive inventory of all the performance mods you have made to the Trans Am.

Nice topic. Sir Can you please make a video on diagnosis and understanding of an alternator. How it works and how to test and how to full field an alternators and other stuff like that related to alternators. Thanks

Where The Hell You Been? LOL ! You got to get something going Dude, been harassing ScannerDanner by watching his older vids and posting! LOL! Only kidding, I know your busy with your real job! If I don't hear from ya, Have a Great THANKS GIVING! GOD BLESS!

Was that an old buick headlight switch?:) hey man, thanks.!

Could u check voltage on d load side of arelay with d volt meter on ohms scale

@5:30 I'm having trouble understanding why you would put 12V at the fuse? Wouldn't there already be 12V at the fuse because you said the fuse is good and there is no open before the fuse. If that's the, all you had to do is simply measure if there is 12V at the switch. It seems to me that putting 12V at the fuse is just unnecessary?

CORRECTION: I was in error in describing the current rating of the coil and the output circuit (contacts). I said that the numbers, such as 20/30, referred to the coil and output current ratings. That was wrong. A rating such as 20/30 means the relay is rated for 20 amps through the Normally Closed contacts and 30 amps through the Normally Open contacts. Sorry for the error.

Hi I'm having a problem with my 2001 Saturn L200. All the interior lights r blinking and security light at the same time also gas and temperature gauge goes up and down. I have a video please watch it called (Saturn Lights Blinking) Thx any info would be appreciated

Gem.

At 6:04 how do you know which wire to poke at with 12v?

cheap aftermarket immobilisers uses basic closed, 12V to open relays. If is immo on, it breaks the ignition, or fuel pump circuit. (on cranking no start the first suspects are these stuffs)

Clicks! Yea we get it! LOL! Something's wrong with you dude! LOL! Great set of vids Matt! I can see that oscilloscope coming! I'm full of suggestions this morning, so here's another, you should warn people that when they are probing sockets/connectors not to push their probes down into the connecter because it will spread them and they will not make contact when you reinstall the relay or what ever you happen to be testing. I know you weren't right! LOL!

Excellent video, however… There’s no way he found a headlight switch for Saab at the parts store. 😂

Great to watch the second part of the series. A few days back I worked on on of my friend's Toyota Corolla 2004 headlights. Head light circuit is a bit confusing sometimes due to the new technology involvement in the newer models. Here is the video link. Give a look please. Regards, kzfaq.info/get/bejne/sMWkmZaezrm2hWQ.html

Just put some volts on them & see if they click.

The people that are saying that you're a great teacher must be your friends because that's the only way somebody would say that. And I'm not sitting here watching this alone I'm watching this with some other men and they're saying the same thing I am

He bought 2 new headlights on the advice of whom? An auto parts store? See this is the crux of the problem. It should be illegal for auto parts stores to give automotive advice. It's a conflict of interest. I think the culture of parts changers begins and ends with automotive parts store. They profit from instigating and catering to bad habits in the same way a drug dealer works. It's actually in their best interest to get you hooked on your bad habit, feed your habit, and keep you coming back for more. They take advantage of people to the point it's now a multi-million dollar business model.

What do you call PRODIGY and INTELLECTUAL AND SUBSTANTIAL add one more KNOWLEDGEABLE the answer is SCHRODINGERS BOX My teacher Thank you very much helpful information video tutorial amazing video brilliant thank you. God bless you and all your family around you and take care and have a great day SCHRODINGERS Box From Nick Ayivor from London England UK 🇬🇧