Troubleshooting Wiring When Running Lights Are Not Working on New Trailer

Question:

my running lights do not work for a new trailer i bought from factory. Wiring diagram is the same as on your website. . Could could it be the ground? I m not familiar with trailer wiring testing.

asked by: Greg

Expert Reply:

The first thing you will need to do is troubleshoot to determine if the problem is with the vehicle or the trailer. To check the wiring, you will need a circuit tester, like part #PTW2993.

You would start by checking the vehicle side. If this was installed aftermarket you will have to test the Modulite or converter.

Make certain you have a good ground by attaching the ground on the tester to the same place the ground wire on the vehicle side of the converter is attached. Turn the lights on the vehicle. Using the circuit tester, you would test the running lights wire (typically Brown) to make sure you have power on the vehicle side of the converter. If you are not getting power at the vehicle side of the converter and you have factory wiring for your harness, check the fuse or relay on your vehicle to make certain they are not bad.

You would then need to check the trailer side of the converter in the same manner. If all functions work on the output side of the converter, you will move on to test the wiring harness. I have linked you to a video that explains how to test and troubleshoot a converter.

If you find any functions do not work, and you are not comfortable with making the corrections, take your vehicle back to the installer and have them correct the issue. If the functions all work correctly on the vehicle plug, you would then concentrate on the trailer.

Check the plug for any signs of rust, damage, or corrosion. If there is no evidence of obvious problems, you will need to use the circuit tester to check the trailer functions. You could run a separate 12 volt battery to test the trailer lights. You would furnish power to the pin for the running lights on the trailer connector to see what lights come on.

Check the ground connection on the trailer for any paint, build-up, or corrosion. Make sure it is securely fastened to a clean metal surface. If you have a plastic license plate holder attached between the trailer frame and a light, this can cause a bad ground connection. If you have an aluminum trailer frame, a trailer with a folding tongue, or a tilt bed, you can run jumper wires from the lights to the main trailer ground to make sure you have a secure ground.

I have attached an FAQ help article for troubleshooting wiring. I have also attached an article that has a trailer wiring diagram.