Hello! I have a 2009 GMC Sierra 3500 HD. It has the 6.6L Duramax. I’m having issues with the trailer wiring harness. The truck has a back rack on it that has the 6” oval brake/signal combos as well as the white reverse. It also has a round 7 plug in the rear bumper. On the back rack, i have running lights on the left side, and signal lights on the left side, but nothing on the right. No signal. No running/brake lights. I have the exact same outcome when a trailer is connected. I’ve checked all the fuses. They’re all good. I’ve checked grounds, and they all appear to be good. What’s happening?

today I pulled apart all the connections for the back rack lights and redid them, and now my reverse lights in my tail lights are staying lit very dim continuously. I’m so lost as to where to look next. Please help!

 

Mate when it comes to problems with trailer wiring harness you can do almost nothing - it's better to go to the pro, as you may be risking your life here.

 

I'm sorry to hear you're having issues with your trailer wiring harness. It sounds like you've already done a lot of troubleshooting, but it's still not working. I think it's worth it to get a professional out to take a look and see if they can help. It might be worth it to get a wiring diagram to see if you can track down the issue yourself. It's also possible it could be a faulty wire or connection somewhere. I'd recommend considering the option of choosing a new lighting system from a reliable supplier. Check out https://www.truckelectrics.com/colle...trailer-lights to find a wide range of trailer lights. I'm sure you'll find the right solution to your issue. Good luck!