No Power to Tail & Brake Lights on 7-Way of 2011 GMC Yukon

Question:

Troubleshooting tail and brake lights not working on trailer. I have a 2011 GMC Yukon Denali. I have 12v power on the 7 way on the tow vehicle. I have hooked up the 2 wires in the engine compartment to stud # 1 and stud # 2. I have checked the trailer fuses in the fuse box, under the hood. Those fuses are good. I have cleaned the ground wire area on the frame of the tow vehicle. Not sure what could be the problem. The tow trailer does not have brakes, so I do not need a brake controller installed. Not sure what else to check. Could it possibly be the PCB relays in the fuse box under the hood? I have also checked the trailer wiring and it is good as well. I do not have power for the tail/marker or brake lights on the tow vehicle 7 way plug.

asked by: Alan R

Expert Reply:

Ok, let's see if we can figure out what's going on here with your tail and brake lights not working on your trailer; you took the right steps so far by checking the fuses, your trailer wires, as well as ensuring you have a good ground. It is possibly the relays, yes, so but I think another possibility is with the 7-way connector on your 2011 GMC Yukon based on you saying "I do not have power for the tail/marker or brake lights on the tow vehicle 7 way plug."

The first thing to do is check your Yukon's 7-way for corrosion, which can be green or white in color, and could be slight but still an issue. A build-up of corrosion can interfere with the signals getting through. I assume your '11 Yukon has the factory tow package so you will also want to unplug the 7-way and check to see if the connecting plugs or any of the wiring is damaged as that can also cause the problem. If there is too much corrosion or damage to the plug itself, what you will need to do is replace the 7-way with the Reese Multi-Plug Wiring Harness for Factory Tow Package # 74682.

If you find it is corrosion, when you get the new plug be sure to use Dielectric Grease for Electrical Connectors # 11755 for added protection. If it isn't the relays or a damaged/corroded connector, there may be an issue with the factory trailer wiring on your Yukon, though hopefully that isn't the case as you'd have to go to the dealer for a fix.

I have added some links below to help articles for you which I also recommend taking a look at.

expert reply by: Kyle S