A 12-volt wire is typically used to power up (or down) high-current devices like an engine, alternator, driveshaft, voltage regulators, starter motors, etc.
It’s always necessary to test the 12v wires when you want to make sure that they carry electricity and don’t break or stop working in any way.
Using a multimeter to test wires is not rocket science. It’s actually quite easy, but there are some basic ground rules you should follow.
Testing the electrical continuity of wires with a multimeter can save you both time and money. There are different ways to test if a 12v wire is live and carries electricity.
The way you test it will depend on the application you are using for this. This tutorial aims to outline the main approaches to testing 12v wires with a multimeter as well as indicate which criteria should be used in each case.
Many times when working on cars, boats, RVs, bikes, etc., you need to know if a wire is live and carries electricity. A multimeter will come in handy for testing the voltage on the wire.
First, you will need to determine if your wire is “hot” or not. If you’re working with a live wire, then it was the negative lead that was grounded. You are likely dealing with a live wire if the wire is insulated.
In this tutorial, we will be using a multimeter to test 12 volt wires to see if they are alive or dead.
How To Test 12v Wires With Multimeter?
Here we will discuss how to test 12v wires to see if they are alive or dead.
How To Test 12v Wires With Multimeter?
- Step 1. Isolate the wire from the power source
The first thing you want to do when testing a live wire is to disconnect it from the power source.
Use a wire cutter and strip off approximately 1–inch of insulation from the black (-) and white (+) wires using a wire stripper.
- Step 2. Test each individual wire for continuity
Some multimeters have an automatic current detector that will tell you if there is continuity, and some do not. Whether you have one or the other will determine which method to use for testing your wire.
If you have an auto-detect continuity function on your multimeter, follow these steps:
Put the black (-) lead of the multimeter on one end of the wire and check for a reading. If there’s no reading, then the wire is broken.
Put the red (+) lead of the multimeter on both ends of the wire. If there’s continuity between the two ends of the wire, then it’s alive.
You can also use a plier and touch both ends of the wire with it to check if it’s alive or dead. If you get a spark, then the wire is alive and carrying electricity. If not, then it’s dead or broken somewhere along its length.
- Step 3. Determine which end of the wire is live or dead
When you test the 12v wires with a multimeter, you will find that one end of the wire is dead.
That end where there was no reading for continuity would be the negative (-) side of the circuit, which means that it connects to the ground.
The other end of the wire on which you got a reading would be the positive (+) side of the circuit and it’s also known as the switched power.
- Step 4. Disconnect the dead end of the wire from the ground.
Now that you’ve determined which side of the wire is live and negative, get your pliers and cut off the dead end.
You can also get another piece of 12v wire and strip it so that you can connect both pieces together. If one end of a wire has continuity on your multimeter, then it’s dead.
Finally, take the wire you just cut and strip the insulation off, and connect it to the other piece of wire.
Make sure that both pieces are facing in the same direction and plug them back into their respective slots. You can screw down your ground wire if your vehicle requires grounding.
Note: Now test your new wire again. If it’s alive, then you should get a reading on your multimeter when you test it. If not, then there’s something else wrong with the wire or it has broken somewhere along its length.
How to Check for a Broken Wire with a Multimeter?
To check the broken wire, you will need to connect the negative (-) lead of your multimeter to one end of the wire and see if there’s continuity.
The positive (+) lead should be connected to both ends of the wire where you strip off insulation about 1 inch in length. If there is no reading on the meter then that means that there’s no continuity and the wire is broken.
1. Remove the insulation from wires about 1 inch in length.
2. Connect negative (-) lead of multimeter to one end of the wire, positive (+) lead to another end of the wire.
3. Test for continuity (the meter will display number). If there’s no reading, then the wire is broken.
Now that you know how to test for live wires and broken wires, you won’t have any problems checking out your vehicle’s wiring system or repairing it as needed.
Just remember to keep those tools in good working order and keep them where they belong; at the bottom of your toolbox.
So now you know how to test the 12v wires with a multimeter and find which end of the wire is live it’s time to fix or replace them.
Before done, don’t forget to check all your fuses, especially the ones that are under or near your dashboard. If your vehicle’s wiring isn’t right up to par, then it might be time for an upgrade.
Make sure you do not lose any screws when disconnecting your ground cable because if you need to re-connect it you will not be able to unless they are available.
Before finalizing the job, make sure that your ground cable is connected correctly to its corresponding screw.
If you find any wires that are burned or corroded, then it’s time to replace them with new ones.
Also, try to check out if any of the metal parts have green liquid stuff on them because this liquid could be battery acid which may have leaked out of the battery.
Frequently Asked Questions
The black wire is usually always negative, no matter what the voltage is. A red wire (or any color for that matter) will be positive.
No, if you do this, you will create an electrical hazard and even possibly damage your vehicle. It’s best to hook up all 12-volt wires with care.
You can use a jumper cable and jump the battery from another car in order to test the 12 volts on your own vehicle if you’re sure that everything else in your vehicle is working properly otherwise.
It doesn’t really matter which one you use because in most cases it’s not going to make much of a difference anyway.
Whichever lead you want to use is up to your discretion. Some people like using the negative lead while others like to use the positive.
If the wire is partially broken, then you can usually repair it yourself. Sometimes a few strands of wire might be exposed and if that’s the case, then all you need to do is twist them together and apply some electrical tape so the area doesn’t get wet or corroded.
Another option is to strip a bit of insulation from the wire and then solder it. If you don’t know how to do any of these, then bring your vehicle to an auto shop for professional help.
You will need to make sure that the multimeter you’re using can read resistance as well as continuity.
In order to check for a short circuit, place one lead of your meter on each side of the dead wire and see if there’s any reading at all on the meter. If you have a short, then it should show a very low reading or no reading at all.
You can use a 12v hotwire to check your vehicle’s wiring. Just connect the positive lead of the hot wire to one end of the broken wire while pointing it at each point in your vehicle where there might be live wires with continuity.
If you see sparks, then that means there’s an electrical short somewhere in that area.
No, you will need a multimeter to do this. You can use a hotwire or jump wire but those only work as temporary fixes and they’re good for testing certain wires that don’t require much amperage.
If your car is not running and if it’s dark, then try turning on the headlights or parking lights. They should dim when the motor is turned off. If they don’t dim, then there may be a problem with your battery or alternator.
Otherwise, all you need is a flashlight and some electrical tape. Unplug your car’s headlight switch and turn on the light with the switch turned off.
If it doesn’t go out, then you know there’s either a broken wire in the headlight wiring or that the unit itself needs to be replaced.
I am Baker Hughes and I live in the USA. I am an electrical engineer and work with 12 Volt products. I want to explore this section more because it is an area of interest for me that has been developed over time. I have 10 Years of experience with 12 Volt products, specifically wiring, installation, guide, reviews, and troubleshooting.