Trailer Brake Lights Will Not Work on a Trailer Towed by a 2004 Chevy Silverado

Question:

I have a 2004 chevy silverado 1502 will drive I have a 14 foot enclosed trailer for my business I have every light on the trailer working except for brake lights Ive checked every fuse made sure all my grounds were perfect and I just put a new modual on my truckand still no brake lights

asked by: Michael P

Expert Reply:

What you are going to want to do first is determine if the problem is on the truck or on the trailer. To do this disconnect the trailer from the truck. Next use a circuit tester such as # PTW2993 to test the connector on the truck while someone else runs through the lighting functions in the cab of the truck.

If the brake light signal is coming through on the trucks trailer connector then the issue is on the trailer. If it is not coming through then the issue is on the truck.

If it is on the truck you will want to inspect all the wiring connections, which it sounds like you have already done, even going as far as installing a new wiring harness. So it does not sound like that is the issue. You mentioned checking the fuses. Make sure you check any fuse labeled CHMSL (center high mount stop light) or stop light. Also make sure to check anything related to the tow package wiring. Use the owners manual to hunt down the fuse locations.

If the issue is on the trailer check to make sure its connector is clean and free of corrosion inside and out. Also make sure the main trailer connector ground and the grounds for all of the lights are connected to clean and corrosion free bare metal surfaces. Ground issues show up when there is more load on a circuit such as the constant draw of brake lights.

Some lights ground through their mounting hardware so make sure to check those connections as well if you have those types of lights. If the trailer has an aluminum frame, tilt bed, or folding tongue, running jumper ground wires from the lights to the main trailer connector ground can help. If you have recently added a plastic license plate holder between a light ground and the trailer frame that can also interrupt the circuit.

It is also possible that the trailer side connector is not pinned out to match the vehicle side connector. I have included a link to an FAQ article that includes diagrams of how various connectors are pinned out. I have also linked an FAQ on troubleshooting wiring for you.

expert reply by: Michael H