Why Would Trailer Wiring Stop Working When Coupler Is Connected to Ball

Question:

Im pulling my hair out trying to figure out the problem with my trailer lights. Ive tested it with two vehicles and experience the same problem. When the lights are hooked up with the trailer NOT hitched to the car everything works as it should. The moment I lower the trailer and the ball hits the trailer tongue, all trailer lights cut out completely. Raise the trailer off the car, and all lights come on again. Ive checked and relocated the ground with same symptoms. Please point me in the right direction in figuring this out. Thanks in advance

asked by: Kyle

Expert Reply:

Use a circuit tester like part # PTW2993 to touch the trailer frame to test to see if there's voltage on it when you have the trailer disconnected and the lights are working. To me it sounds like you have a short somewhere on the trailers wiring that touches the trailer frame, and since trailers pretty typically will ground through the coupler and hitch when the coupler is lowered on the ball the short is created.

That's really the only way what you described could be going on.

expert reply by: Jameson C