Troubleshooting Right Trailer Brake Light & Trailer Brake Controller Not Working

Question:

i have a 04 silverado 1/2 ton all lights on truck are working, when i plug ANY trailer in have 3 it all the same thing i get left and right turn signals, running lights and only the LEFT brake light? the right brake light is not working but right signal is? also my trailer brake stopped working?? all fuses are good, all connections are good i can plug trailers in to my to my other trucks and every thing is fine? some how the right trailer brake signal is dead along with my brake controller confusing part it the right turn signal works just not the right brake light on the trailer thanks

asked by: Stumped

Expert Reply:

Thanks for providing the details on your trailer wiring issue.

Since you have three trailers that all show the same issue when connected to your 2004 Chevrolet Silverado odds are good that the problem is in the truck wiring.

The first thing to check is the ground connection on the vehicle wiring harness. This wire's ring terminal must make a clean metal-to-metal connection in order to allow for all functions to operate properly. Corrosion can build up and cause issues. Try removing the main ground wire for the vehicle harness, sanding off that point to expose clean bare metal, and re-attaching the ground wire. You can apply dielectric grease like # 11755 to protect that connection from future corrosion.

The next thing to check is the condition of the contacts inside the truck's connector. Corrosion can develop on the outside visible parts of a trailer connector or it can form inside where it is very tough to spot. Sometimes corrosive build-up can cause two adjacent circuits to become bridged together and this can cause a short. You might be able to correct the issue with a spray-on electrical contact cleaner like Caig De-Oxit or a similar product made for cleaning electrical contacts. The corrosion could also be in the connector that plugs in to the 7-way so check that too.

If you refer to the photo I linked for you you'll note that the right stop/turn signal contact is at the 3-o-clock position and just next to it is the brake circuit. If cleaning the trailer connector does not correct the issue you may need to replace it with # HM40975 or # A10-7072VP. Since these two circuits are the ones giving you trouble odds are good there is a short between them.

If you have a circuit tester like # PTW2993 you can test the truck socket's contacts one at a time while a helper turns on the various lighting signals. Use of the tester is demonstrated in the linked video.