Trailer Brake Lights Not Working on a Trailer Towed by 2008 Isuzu N-Series

Question:

2008 isuzu NPR to trailer. All lights and functions work Except Trailer Brake lights. Blinkers flashers ect, all fine but when you step on brakes nothing. There is no fuse in truck for trailer lights., there is a brake controller.

asked by: Tim

Expert Reply:

The turn signals and brake lights should be on the same circuit. What I think may be happening is when the brake lights are on, they draw more power. When more power is drawn, this is usually when you will see ground wiring problems.

First, I would make sure that the vehicle side connector shows the same pin for turn signal and brake lights using a circuit tester like # PTW2993. Next, check to make sure both the trailer side and vehicle side connectors are free of dirt and corrosion.

Then move on to the trailer to check the main ground wire. It should be attached to a clean and corrosion free bare metal surface. The taillights, too, should be grounded to a clear, bare metal surface. Most trailer lights ground through the mounting studs. A ground issue is the most common cause of problems like this.

expert reply by: Michael H