How do you test a trailer harness with a multimeter?

Asked By: Kaddour Chretien | Last Updated: 20th May, 2020
Category: travel camping
4.3/5 (1,904 Views . 13 Votes)
Set your multimeter to read volt DC, connect the black probe to the negative and the red probe to one of the control wires, if your trailer plug is in order, your multimeter should have a reading approximately equal to the volts of your battery. Now apply the same process to the other control pinholes.

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Beside this, how do you test a trailer bulb?

Use a screwdriver to remove the screws in each corner of the faceplate over the light on the trailer. Unscrew the blown bulb and replace it with one of the same voltage. Test the lights again by pressing on the brakes in your tow vehicle. If the light still doesn't come on, you know there is a problem with the wiring.

Likewise, how do you find a short in wiring on a trailer? Use an ohm meter, and check all the wiring for continuity to ground. If your running lights are blowing the fuse, and the brake & turn signals work fine your brown trailer wire is shorted to ground somewhere, or you have a grounded running light on the trailer somewhere.

Likewise, how do you test the ground on a trailer wiring?

Check out the white wire on the trailer to see if it's actually used as a ground (which it should be). Those 4 wires should be green, yellow,brown and white. Check out the white wire on the trailer to see if it's actually used as a ground (which it should be).

How do you test a trailer wiring with a battery?

Step by Step

  1. Using a battery or jump box, connect one end of the black test lead to the negative terminal and the other end to the “Ground” pin.
  2. Connect the second test lead to the positive terminal of the battery or jump box.
  3. Make contact with the alligator clip to the “Left Turn/Stop” pin.

25 Related Question Answers Found

How does a 7 pin trailer plug work?

A 7-Way has these functions and a 12 volt circuit, a circuit for electric trailer brakes (requires a brake controller in the vehicle), and a reverse light or auxiliary power circuit. There are other types of connectors as well.

Why don't my running lights work on my trailer?

If there is no power on the running light pin then there is a break or loose connection somewhere between the connector and where it terminates at the front of the vehicle that you will need to track down. Running jumper wires from the light grounds to the main trailer connector ground can help.

Are trailer lights AC or DC?

All the trailer lights run on 12v DC power – even while connected to AC shore power. The AC power goes to a power converter that transforms the AC current to DC to run lights, water pump and maintain a charge on your battery.

How do I rewire my trailer brakes?

If the trailer wiring is running down the left side of the trailer, then we splice the left side brake assemblies into the main electric brake power wire coming from the 7-way connector. We then run a jumper wire from the electric brake power wire to the right side brake assemblies (see photo).

What is the color code for trailer wiring?


Brown wire to the tail or parking lights. Green wire to right turn signal/brake light. Yellow wire to the left turn signal/brake light. White wire to common or chassis ground.

How do you fix trailer brakes?

How to Repair Electric Trailer Brakes
  1. Open the trailer connector.
  2. Locate the wire that controls the electric brakes.
  3. Plug the trailer connector into the tow vehicle connector and have an assistant press the brake pedal.
  4. Attach a 12-volt test light's ground clip to a bare metal portion of the trailer's frame.

How do you test an electric brake controller without a trailer?

How to Check a Brake Controller Without a Trailer
  1. Press down on the brake pedal while watching the brake controller.
  2. Check the fuse to the controller if the display does not light up.
  3. Go to the trailer connector on the back of the tow vehicle with your multimeter.

How do you ground a trailer light?

Each lamp needs to be grounded either through its mounting studs being in direct contact with the trailer frame or by having a jumper wire ran from the lamp to the trailer frame. Ground the trailer connector at the front of the trailer, which will use the trailer frame as a ground wire.

Does trailer have to be on ball for lights to work?

In some cases trailer lighting will ground through the hitch ball but that's typically only if the actual ground circuit is insufficient. It needs to ground through the wiring of the trailer harness.

How do you test a 4 way trailer plug?


How to Test a 4-Prong Trailer Connector Plug
  1. Tell your helper to turn on the ignition while you go to the connector plug.
  2. Tell your helper to turn on the right turn signal.
  3. Tell your helper to turn on the left turn signal.
  4. Tell your helper to shut off the turn signal and step on the brake.
  5. Tell your helper to release the brake and turn on the lights.

How do you test an electric trailer brake controller?

Testing the brake controller is fairly easy. Sever the blue brake output wire near the brake controller leaving enough room to reconnect it and then apply the manual slide. Using a circuit tester like the Quickee Tester, part # 3808, you should get output to the controller side of the wire you severed.

Do LED trailer lights need to be grounded?

Yes, all of the lights in the #TL16RK Waterproof, Over 80 inch Trailer Light Kit will need to be grounded. Some trailers will actually end up grounding through the coupler, to the ball of the ball mount, to the hitch, and then to the frame of the tow vehicle.

Can you use a multimeter to test a light bulb?

You can check a light bulb with a multimeter. But virtually any incandescent filament bulb can be tested in the way that is described. This will be particularly useful for checking flashlight bulbs because the filaments are very tiny and difficult to see.