Right Brake Light on Trailer Not Working when Connected to a 2011 GMC Canyon

Question:

Can you help me determine the solution to my problem? I have a 2011 GMC Canyon with the appropriate Curt 4-plug trailer connector. It has worked perfectly when using my father-in-laws trailer for the past 6 years, First use this year, all lights worked except I do not get a right brake light on the trailer. The right turn signal and tail light functions are good, just not the brake light. My voltage tester shows 11.7 volts on both the green and yellow port when the brakes are applied. I had a local U-Haul dealer test the outlet on the truck and he said everything tested fine. He said the trailer is the problem. However, when we hook up the trailer to my father-in-laws vehicle, the right brake light function works fine for him. Any ideas as to why it is not working with my truck? Thanks.

asked by: David H

Helpful Expert Reply:

This sounds like a ground issue. Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light but can show up any time. Some vehicles can overcome a weak ground which could be why it works with a different vehicle.

Make sure that the vehicle side and trailer side connectors are 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