Troubleshooting 7-Way Trailer Connector Issues On 2004 GMC Sierra

Question:

I have a 04 GMC Sierra and the pin on the seven way connector activates when I turn on the tail lights. Can anyone tell me why this is happening.

asked by: Rick

Expert Reply:

If you have the wrong pin activated when you turn the lights on, then there may be a ground issue. Check the wiring for any signs of damage or pinched wires and make sure the trailer connectors are free of rust or corrosion.

If everything checks out physically, then I recommend checking the wiring with a circuit tester like part # PTW2993. Have someone sit in the cab and run through the functions as you test the trailer connector when the trailer is not hooked up.

If the truck wiring all checks out, you can move to the trailer and test the wires there with a 12V battery. You can use a spare battery, or you can use a set of jumper cables with short lengths of wire. Just connect the battery negative to the trailer plug's ground pin. Then check each pin with the jumper wire from the positive battery post. I have attached a helpful article on trailer wiring you can check out.

expert reply by: Jeffrey L