Troubleshooting GMC Truck Where Trailer Brake Lights Aren't Working

Question:

2002 gmc Sierra 4×4. Brake lights work on truck, brake lights on trailer did work until recently. Everything else works on trailer, turn signals, running lights. I checked for power at the trucks plug and there isnt power on either brake pin, left or right side. I have a perfect ground. Is there a fuse on the truck just for brake lights? There is an electric brake that is hooked up on trailer that works fine also. Its 7 wires on the truck plug. But only 5 wires on trailer side. Any ideas would be highly appreciated. Ive been trying to figure it out for 3 days.

asked by: Dave

Expert Reply:

What you described sounds like a blown third brake light fuse or CHMSL fuse. Check the third brake light of your GMC Sierra and it most likely won't be lighting up with the brakes. This is a very common problem with the GM trucks of around your year.

expert reply by: Jameson C