DIY Video: How to use a multimeter


Does the wiring in your classic car look like a plate of spaghetti? Wiring is something many owners are scared of, but we are here to help. Prepare to dive into electrical projects by getting familiar with a multimeter. This simple and affordable tool can be your lifeline in solving electrical problems for vintage rides. Hagerty’s Matt Lewis talks you through how to troubleshoot electrical gremlins like a professional by testing for voltage, ohms, and amperage. Hopefully this will spark your motivation!

This is a companion discussion topic for the original entry at https://www.hagerty.com/articles-videos/articles/2018/07/06/diy-how-to-use-a-multimeter


Great video! A multi-meter (aka DMM- since I still have an analog unit) is the most used tool I have in my toolbox.
Many other uses include “voltage drop”. Low volt settings on DMM to see if components are bad, but still work. Like switches, relays or lengths of wire. Testing voltage from one end of wire or across a switch or fuse to the other should give minimal drop. This causes havoc in newer cars where 3/10v or more will give you big problems. Lose 1v and you can toss the part. If a car batteries when cranking fall below 10v… It won’t make it through the next winter.
Oh, yeah- I have owned many Triumphs, and many multi-meters have saved the day.


Might be helpful to point out to the novice that the light being used in this video may not be “typical” to what is found on most “vintage” cars. A light socket with two positive terminals, with two conductors (one being a ground) is unusual. This light must be plastic since a negative/ground conductor has been supplied. Most “vintage” lamp assemblies with the two positive terminals will have two conductors but both will be attached to those positive posts and the “metal” housing will be the “negative” terminal. Testing across the two “positive” terminals will NEVER produce a circuit or continuity.
Surprised this fixture (being plastic) didn’t have 3 conductors. One negative/ground, one conductor for each filament in the lamp.


That lamp actually grounds through the mounting hardware. Both those leads; the black and the red are hot leads to the bulb bottom contacts. When he put power across the two leads he energized both filaments linked by the ungrounded ground.


I see(about the ground path) and stand corrected on the continuity issue. As a retired electrician, however, that would be a strange way of troubleshooting a “tail light” that is not working. I would be measuring from “ground” to the tail light conductor instead of across the brake and tail light leads. Testing the lamp filaments would be done at the base of the lamp. Whatever works. Just question the best method to teach since this video is supposed to “instruct”.


Hi… I have a projector with an LED chip lamp. I want to measure the current output of the projector’s power supply and thus ascertain the LED’s wattage.How can I measure current output without a multimeter? One unscientific method is to light the LED using a known power supply and compare it to the brightness of the unknown power supply. I also don’t have a light meter
How much is it okay to overload an LED chip lamp? Like if it’s rated for 20W can I give it 30W with enough cooling?

printed circuit assemblies


Thanks for pointing these things out. Allow me to shed some light (pun 100% intended) on the situation here.

  1. Yes, both the black and red wires on this housing were connected to the power side of each filament for the bulb.

  1. Yes, the way in which I tested the bulb was through both filaments, with the common ground completing the circuit.
    (In hindsight, this could have been done differently)

  1. This particular replacement light housing is incredibly odd in my opinion. The wiring assumed a chassis ground, but every mounting point was painted, which would insulate the ground and keep the bulb from lighting. I attempted to research the part number of the housing (Grote-5085), but couldn’t find the exact same bracketry anywhere.

If anyone has more information, please share it. I’d love to know more.

  1. I was not aware the light was a dual filament style until we had already started shooting the video.
    (I’m surprised it wasn’t three wires as well)

At the end of the day, I think the way I demonstrated voltage, amperage, and resistance worked just fine even though the bulb wiring was not perfect. I promise to be more diligent in future videos.

Thanks for watching!


Good ‘primer’ for using a multi-meter for basic trouble shooting…
while it wasn’t covered here, the AC side of your meter is quite useful when chasing charging system ‘gremlins’.


Thanks Matt. No hostility intended. Only trying to help clarify for the novice.

This product looks like something made by foreign workers who have no idea how it’s supposed to work and don’t much care. Unfortunate. ;o(