Troubleshooting Vehicle Brake Lights Not Working & Trailer Brake Lights Work 2007 GMC Sierra 3500

Published 09/08/2023

Question:

I have a trailer wiring harness made by Hopkins for my 07 GMC Sierra Classic 3500 cab and chassic. It is a plug and play deal. The red, yellow and green coming from the first plug does not go through the converter but to a plate with three mini tunnel looking components and then to ground. Also the white ground wire on the down stream side of the converter is clipped off. Thanks. What ever is wrong I have no brake lights on the truck but do have them on the trailer.

asked by: David C

Expert Reply:

First I recommend checking your fuse panels on your 2007 GMC Sierra Classic 3500 cab and chassis. You will want to use a fuse tester like the one in the Kit # PT36ZR to check any fuses which have to do with the factory brake lights on your truck. I do see there are separate fuses for the trailer wiring and the vehicle lights which could be your issue. Also and just to verify you will want to check the bulbs themselves to ensure they did not burn out. If this is not helpful please send me some images of your wiring so I can fully understand what you have as I do not see any aftermarket parts from Hopkins which sounds like what you have.

expert reply by: Bud M