Troubleshooting Trailer Lights that Stop Working When Headlights Come On

Question:

I installed the above harness in my 03 Liderty, and all worked ok, breaks and turn sigs. Bur when I turned on the head lights, the canceled everything out. So it works fine as long as I dont turn on tne lights. Is the module defective? Thank you

asked by: Bill S

Expert Reply:

The problem you are having is a classic ground issue. If the ground wire to the trailer frame or the tail light grounds are not connected securely to clean, rust and paint free surfaces then when the headlights are turned the extra amperage draw for the running lights will cause all sorts of lighting issues.

I would start by removing the ground wire at the trailer coupler and cleaning up the connection point and re-securing it to the trailer frame. Next I would check the ground connection of the trailer lights. Usually they are grounded through the mounting bolts for the lights. Make sure that the connection is clean and free of paint, rust and debris and, if there is a plastic license plate holder on the drivers side, make sure that it is not inhibiting the lights ground. Finally if the trailer light mounting brackets are bolted to the trailer frame you should remove them clean up that connection point also.

These simple steps should get you going and ensure that your trailer lights will work properly.

expert reply by: Jameson C