Troubleshooting Malfunctioning Right Brake Lamp on Trailer Towed by 2005 GMC Yukon

Question:

05 gmc yukon seven way plug works for everything but the rt brake light all wires look good fuses are good

asked by: Jason C

Expert Reply:

Since the right turn and brake lamp signal are carried on the same circuit, the problem is most likely in the vehicle wiring. Begin by using a circuit tester like # PTW2993 on the right turn/brake lamp pin in the 3:00 position on the 7-way. You should get signal on that pin when the brake pedal is pressed. If you don't, access the wiring harness behind the 7-way, and look for the green wire in the wire loom. Use the tester while the brake pedal's being pressed. If you see signal on the wire, you've confirmed that the 7-way is faulty. Clean or replace with # HM40975 as needed.

If you don't get signal on the wire, recheck the fuses. If all's okay with the fuses, you have broken wire somewhere between the fuse box and the trailer connector.

I've linked you to a trailer wiring troubleshooting FAQ article that I hope you'll find helpful.

If your trailer lamps use incandescent bulbs, I'd also recommend checking the bulb and the socket the bulb installs into.

expert reply by: Mike L