Trailer Running Lights Do Not Turn On

Question:

I have , I believe a 7 plug wiring harness on my trailer. The brake lights and the turn signals all work but I dont have any running lights.

asked by: Greg M

Expert Reply:

To determine where the problem is there are some easy tests that you can perform. First, disconnect the trailer from the tow vehicle. Then you will need to use a circuit tester such as # PTW2993 to test the vehicle side connector. If it is a 7-Way, the running light circuit will be the pin in the 11 o'clock position.

If you are not getting power there when the vehicle head lights are on then the issue is on the vehicle side. It could be as simple as a tow package fuse or relay (use the owners manual to find the tow package fuse/relays locations). Also make sure the trailer connector is clean and free of corrosion at the pins and in back where the wires attach.

If the vehicle connector works fine then the issue is on the trailer side. Probably a ground issue. Make sure that the trailer side connector is also clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces.

The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

expert reply by: Michael H