Troubleshooting Trailer Connector on 2004 Chevy Silverado

Published 04/25/2015

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Question:

I have a 2004 3500 dually Chevrolet long box have always had lights to my trailer plugged in and nothing I am thinking for all the lights to not work it is my ground where do they ground the trailer connector to my truck do they run a wire to my batteries diesel

asked by: Tom W

Helpful Expert Reply:

The first thing you'll want to do is determine if the problem lies with the trailer or the truck.

Can you try the trailer with another truck or the truck with another trailer? That'll tell you pretty quickly where the problem lies. Another option would be to use a circuit tester like part # PTW2993. Have a helper activate all the taillight functions one by one, as you test the pins on the trailer connector. I'll link you to an FAQ article that shows what signal you should be getting on which pin.

If you're not getting any signal at all, or if they're erratic, it could very well be a poor ground. The trailer connector on the vehicle is usually grounded to the vehicle frame somewhere at the back of the vehicle. You can trace the wiring harness from the trailer connector to find the grounding point, and make sure its tight and not corroded. Also test the ground on the trailer, which is usually found on the trailer tongue.

Check the trailer connector on the truck and the trailer. If it's corroded or damaged, you'll want to replace it. The # HM40975 would be an excellent choice.

If the grounds are good, there might be blown tow package fuses. The fuses are located in the fuse box under the hood on the driver's side inner fender. The lid of the fuse box will have a diagram showing which fuse protects which circuits.

I'll also link you to our trailer connector troubleshooting FAQ article.

expert reply by: Mike L