Multimeter basics for automotive use | Hagerty DIY

Multimeter basics for automotive use | Hagerty DIY


– Hi everybody. I’m Matt Lewis with
Hagerty and in today’s DIY, I’m gonna talk about the
basics of using a multimeter. When you’re looking at multimeters, there’s a lot of different options. We’ve got very small pocket sized deals, very expensive professional tools, and then you can get in to
just the average multimeter. This one here is great because it’s got all of the options you’re gonna need for checking the electrical
system on your automobile. A little multimeter like this is available in a lot of different places. You can find them at hardware stores, you can find them at auto part stores, you can even find them at
home improvement stores or anywhere online. An item like this which is
great for the DIY home use, $20-$25 it’s gonna do
almost everything you need from a day to day usage. Now that we have our multimeter open, you can see there’s lots of
options as to what you can test and actually, more
connections on the front than there are leads that come with it. We’re gonna be focusing on DC voltage, ohms or resistance, and amperage. Depending on what we’re testing, we’re gonna be plugging the leans into these different terminals. We’ve only got one black terminal on here so that’s obviously going
to be our ground lead. First thing we’re gonna
be working with is voltage so I’m gonna go ahead and plug it into this one labeled voltage. For the sake of testing voltage, I’ve got a little battery
here hooked up to these leads. Since there’s actually electricity at the end of these leads,
I’ve put down some cardboard so our metal table doesn’t start conducting. With this multimeter, there are multiple options for voltage. What it does is it basically moves the decimal point around here. We know that cars are 12 to 15 volts depending on the situation so our 20 volt max setting is gonna be plenty for what we’re working with
on the automobile here. You can move it up to 200 which you see just jumps this decimal point, and even to 500 which
eliminates the decimal point. While you gain head room for voltage, you lose accuracy because you can’t see portions of a volt
at the 500 volt setting. At 20, we’re great. We know we’re not gonna exceed 20 volts and we get plenty of accuracy with to the hundredths of a volt. I am gonna warn you that electric cars run super high voltage,
enough to be lethal. If you have an electric or a hybrid, I would advise just taking it to a shop. Don’t mess around with the electrical system on it because it is dangerous. When you’re testing voltage on a car, you’re gonna remember that this black lead is going to be
your negative terminal. That’s gonna be the ground. We’re gonna go ahead and hook it up to our pigtail here with the black. This red one is gonna be
the positive terminal. That, we’re gonna wanna
hook up to our positive. Here we see, this little battery I have is reading 13.81 volts. That’s pretty normal for a 12 volt system to actually read higher than 12 volts. A regular car battery’s gonna be between 12 and 13 if it’s functioning properly with the car off. When the car’s running, your
charging system kicks in, you might see anywhere from 14 to 15 volts depending on what your alternator or generator is currently doing. When we’re talking about voltage, what we’re actually looking at is the electrical charge difference between the negative terminal of a battery and the positive terminal
of a battery or a circuit. A good analogy for that
is like water pressure. When you’re looking at
the water in your home, how much pressure does it have? Next thing we’re gonna
talk about is amperage. You can consider amperage
like the flow rate, so how much water is actually
coming through the system. For amperage, I am gonna have
to move this terminal over from our voltage setting
to our amperage setting just like this and I’m gonna have to swing our dial over to
the DC 10 amps setting. This is gonna allow us to measure amperage instead of
voltage on this circuit. When you go to measure
amperage on a circuit, you do actually have to
disconnect the circuit and put the multimeter in between the power and the load
or light in this case. I hooked up the red lead to the positive and I’m gonna hook up the black lead to our red lead here which will complete our circuit
and turn the light on. Pulling just over half of an amp. We’ve tested the voltage of our battery, we’ve tested the amperage of the circuit with the light bulb on. The final setting we’re gonna talk about is this ohm or resistance setting. What that is is it measures how difficult it is for electricity to
pass through way circuit. When we’re looking at a little
piece of wire like this, this is just copper wire, this should be almost zero
ohms or zero resistance meaning it’s very easy for electricity
to flow through it. If we go ahead and hook
our terminals up here, once this settles we’re at .3 ohms. This may just be a variance of what the multimeter can read because this is a fairly inexpensive multimeter. It may be this does have a tiny
bit of resistance in it but, basically we’re looking for a very small number when you’re reading something like just a piece of wire. Right here I’ve got what
is an ignition coil, I believe it’s off of a little motorcycle, and measuring across these two points, we’re gonna see how easy it is for the electricity to flow from side to side. We hook this up and we see
about five and a half ohms. That’s more difficult for electricity to flow than just this piece
of wire but, still fairly easy. That’s not a lot of ohms. For the sake of testing all three things we’ve talked about today, I’ve gone ahead and made
our light bulb broken. This light doesn’t function anymore. We hook power up to it. There’s no light. First thing we’ll test is voltage. We’ve got our voltage set back up, we’ll hook up to the negative terminal and positive terminal. Electricity is getting to
this point in the light bulb. Next thing we’ll test is amperage to see if that electricity is actually flowing through the light bulb. Go ahead and switch that over to amperage, move our terminal over
to the amperage terminal, and we remember we put the amperage in line with our circuit. Go ahead and hook this up. It’s reading nothing. I know that this circuit
is not completing, meaning there’s something
wrong inside the bulb. The final test we can do is our ohm test. We’ll go ahead and move this back to ohms. We’ll put our meter back on ohms. We’ll go ahead and hook this
up and it appears to be open. The meter didn’t even react. What that means is there is nothing connecting this wire and this wire and that’s why the bulb’s not lighting up. Now we know we’re gonna
need a new bulb in here because the electricity can no longer flow through it causing it to light. We can replace this bulb and
just see if we can fix it. For the sake of troubleshooting, what we’re gonna do is we’re gonna actually measure the
ohms of this light bulb. The way you do this is these
bulbs, this is an 1157 bulb. It’s super common for cars. This outside ring here
is the negative terminal and then what you have is
two positive terminals. It’s called a dual filament bulb. If you look really close you can see there’s actually two filament sections. Those are what produce the light. We’re still on our ohm setting so we’re gonna go ahead and
connect to the negative and then probe this positive. It didn’t even react when I hooked it up. There could be a couple of issues. These connectors here that
hook the socket to the bulb might be corroded or broken, this outside may no longer be grounding properly to our negative terminal, or really where these wires go in may be broken or kind of anywhere within this circuit it may be broken. We grab a new bulb, we put it in. Now we can use the same ohm
test, hook up to our terminals. We’re seeing the numbers responding which means electricity can
flow through this circuit now. What that means is we have a good bulb and a good housing with good wiring. Now that we’ve fixed it, if we hook our battery
up, we have light again. If you find yourself with a brand new multimeter that you want to play with, you can do it with something as simple as a double A battery. Here we’ve got a positive
terminal labeled, it says it’s gonna be 1.5 volts. You can hook that up and play with that. I hope this multimeter DIY was helpful. If you have any comments or questions, go ahead and post them below. Make sure to subscribe to our channel so you know whenever
we put out a new video and we’ll see you next time.

About the Author: Michael Flood

52 Comments

  1. None of this makes sense you are fucking with the bulb after disabling it and you say on the wires you have a ground and power but not how you determined that on the battery and now you are saying the round housing that the bulb goes into is a ground so you now have a power, two grounds and no neutral wire to complete the circuit? Also what is the difference between a amp and volt what is a watt what is the difference between them and how do you determine each?

  2. Very good information if you are a car guy or hobbyist like myself it's very important to learn the multimeter I learned it pretty good and it helped me a whole lot putting the whole electrical system together for my 67 Firebird love you guys I Hagerty keep up the great job

  3. This is a great video. I'd like to see a follow up video that details real world situations with corrosion on bulb sockets. It would be great to see how to measure resistance in a socket that is corroded that explains how to troubleshoot older wiring that might be susceptible to corrosion. An explanation of resistance metering in more detail would be helpful for the DIY crowd that is trying to determine why, for example, a turn signal bulb is working but flashing faster than the other side of the car. Measuring resistance would be a way to determine that the circuit can flow electricity via amps and voltage yet resistance is higher than normal which might be the cause of why the turn signal circuit is behaving erratically. This just happened to me last week and I spent hours learning about it when I bet one of these awesome simple videos would detail a more real-world scenario.

    I can't say enough how much I learn from these Hagerty DIY videos. Thank you very much!

  4. I love how in American accent it's a molt-ay-mee-tur so used to it being a molt-ee-mee-tur in the UK. Cool video though!

  5. I use a mulitmeter so seldom that I have to stop and think twice about it each time I use it. These are good refresher tips for me regarding a very useful tool.

  6. This is a very helpful and informative video on Multimeter function. It was a huge help for me and I am sure it will help hundreds if not thousands of others. Thank you

  7. Using your fingers to hold the wires onto the test lead is a bad habit to get into. I was checking trailer wiring and a short made the wire get red hot. I got a nice brand on that one. It also trains you to get bit when you start working with AC circuits.

    Otherwise a lot of good info.

  8. This was such a massive help in learning about how a multimeter works. Please do more of these types of videos!!

  9. Good analogy of amperes and voltage but I must disagree with you about the black wire. You were right at one point calling it the negative. You were wrong when you called it both the neutral and the ground. It is in fact neither ground or neutral.

  10. Good info Matt, just keep in mind, you are assuming that your viewers are using 12v negative ground….but this is a Hagerty video, and many customers of Hagerty have 6v positive ground classic/historical vehicles….

  11. What about a VERY important warning about exceeding the rated current draw when measuring amps on an unfused meter such as the one you used. Goodbye meter if you do.

  12. Good little intro to multimeters video. I think what I found most interesting…towel bar bumpers on a Super Beetle!

  13. I used to work at a parts store. Customers used to come in trying to have me help them diagnose their electrical problem. I would say just buy a multi meter and watch a YouTube video on how to use it for cars. 9 times out of 10 the customer would say I'm not gonna do that nato pay some absorbent thi to have an electrical expert look at it. This is the M1A the most important diagnostic tools right up there with an OBD

  14. DMMs are a necessity for automotive electronic diagnosis. That being said, most malfunctions are simply opens and shorts, and tracking them down can be done with a very simple 12VDC test light.

  15. This was helpful, but just scratched the surface. A series of videos on using the multimeter would be a real service. Thanks.

  16. Only parts of electric cars run on voltage above 42 volts DC, which is considered by the SAE the cutoff point above which a man could be electrocuted. Many circuits on electric cars are still 12 volts DC. Use a meter and a service manual.

  17. I've recently purchased a 1948 Chrysler. It's a 6 volt system and positive ground. I suspect that I would use a test light in the usual way. Alligator clip to ground on the car and probe to where power should be and the bulb will light up. I'm guessing if the tester is 12 volts the light will just be dimmer.
    But if I'm trying to track down a non working item like lets say a tail light with similar issues as in your video. How do I use the meter? Does black still go to ground, or does red now go to ground? When testing amps and ohms, do I do anything different?

  18. thank you! do you need to change the inputs of your multimeter when you measure current instead of voltage also? thanks!

  19. And the real question is…What is that symbol next to the 2volts DCV that says "POINTS" I've had the 3300 for years and still have no idea why that symbol is there, what it means, and what "points" are.

    If anyone knows it will be amazing as Google had failed me with searches for years. Now I look for YouTube videos with Innova 3300 meters and ask there. How Innova stamps something on their meter and doesn't say what it means in the manual blows my mind.

  20. educate me please..once i knew about how ohm.meter works, yet a TBI puts lots 'grey' an require refresh.. objective is 96jeep sport cherokee electric windows StayUP cooks brain103*. the door panel driver side off. is problem (switch-or door.motor?) im ready IF must run wire direct from battery.

  21. Thanks for the video, I have a question, which book do you suggest to understand automobile electric , simple explanations and understandable , that will make me understand the full automobile electric circuit to test parts wires fuses etc , i will appreciated so very much since i am starting this new business!!!

  22. Thank you for this video. I would have understood it a lot better though if you had used an actual car to demonstrate the tests. Using a standalone light bulb lost me completely. I am a visual learner, but I need to see it hands-on.

  23. Fantastic Video. I'm a DIY kind of backyard mechanic and pretty knowledgeable about numerous aspects of cars but I was always a little unsure of the electrical side of things and especially on how to test and probe for electrical issues. You made the information as easy as pie. Great job and I really appreciate it.

  24. Matt,
    What is a decent auto-ranging meter w/the beep for resistance? I can't figure out what's wrong, so i have to test the tps, idle air control valve, cts, etc. on an 88 sentra w/ tbi, and I know very little about these cars. I'm used to working on my Chevelle.
    Thanx.

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