How to test trailer lights with a multimeter

How to test trailer lights with a multimeter. Don’t you think it’s inappropriate to dodge in traffic without brake lights, right and left lights, and running lights?

Most of the time, exposure to the sun, grime, grit, snow, rain, and dirt can cause serious adverse effects and let the trailer lights to create faults.

Fixing trailer lights is an essential part of their upkeep and is a vital step towards ensuring the safety of the driver and the vehicle.

There are many reasons why a trailer light may not be working, so; the first step is to diagnose the issue. A multimeter will act as a blessing in diagnosing the cause behind any culprit. 

How to test trailer lights with a multimetertest trailer lights with a multimeter

We’ve compiled enough information regarding how to test trailer lights with a multimeter so that you can avoid any future errors and perform the task in a more precise manner. 


The first step toward checking a trailer light is to know the root cause of the problem. A few of the issues can be:

  • Burned-out light bulb
  • Connectivity issues in the wiring system

This can be checked by connecting the lights directly to the tow vehicle, steering the car right or left, applying brakes, or performing the respective function the light turns on while performing. 

Grounding test

Now, the ground connection is to be tested using the Multimeter. Take the two probes of the Multimeter, which are black and red or negative and positive, respectively.

The Multimeter should be on the Ohms or resistance setting for ground testing. Place probes together to ensure that they work.

Attach the red probe on your grounding and black search to the negative terminal. The Multimeter should read about 0.3 ohms for grounding. 

Testing Trailer plugs

You should test the trailer plugs to see if grounding is sufficient. You have to try if the trailer plug is receiving voltage. Turn signals and brake lights are used together, so there is four wires total.

These will be tested separately to check for any issues and errors correctly. To try plugs, turn the Multimeter to volt settings.

Connect the black probe to negative settings and the other multimeter probe to one of the positive settings and turn the light controlled by that pin on. 

If the Multimeter reads the same as the number of volts the plug being tested is, that specific plug is not the reason for the malfunction.

For example, Connect the red probe of the Multimeter to the control of the proper signal and then turn on the right light.

If your light is 14 volts and the meter shows a reading of 14 volts, then the fault is not within your plugs. 

Testing lighting connector

The next test is carried out to check the problem with the wiring. To do so, put the Multimeter on resistivity settings. Take out your trailer connector and ensure your wires are attached correctly to the Multimeter.

Place the red probe on the ground connection and black on-point pins. For cables that have more than one control, they should first be disconnected and tested individually. 

A sound wiring system shows a reading of about 3 ohms. The wiring system can be connected to more than one control.

So to make sure every control is being tested properly, you should check individually to rule out any possibility of faults. 


How to test trailer lights with a multimeter. It can be concluded that testing a trailer light can be pretty simple if a proper diagnostic is performed. All the ways to solve different complications are listed above.

We hope we’ve succeeded in explaining and some factors to consider when initiating the process.

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