Troubleshooting Trailer that Keeps Blowing Running Light Fuse on Truck

Updated 07/07/2017 | Published 07/06/2017

Question:

Hi,I have a 2008 Chevy 3500 that keeps blowing the trailer running light fuse. I have tried everything under the sun almost, even had my truck in by the dealer to make sure it wasnt the trucks fault. I am suspicious that it has to do with my trailer brake battery. So, my question is,,,, Can a bad trailer brake battery keep blowing that fuse? Because it only blows after you brake a number of rounds. Otherwise turn/brake etc still works. If that doesnt fix it then next step is to replace the running light wire on the trailer, though I checked it and couldnt find anything wrong with it

asked by: David J

Helpful Expert Reply:

The breakaway battery on your trailer shouldn't be connected to the running lights. It should get power from the 12-volt pin and then apply power to the brakes if/when the pin is pulled.

It sounds to me like you have a short on the running light circuit, brake light circuit, or both. Since the problem happens after the brakes are used, I lean towards the brake light circuit.

Even though the truck was checked I'd replace the fuse and test at its trailer connector using a circuit tester like # PTW2993.

After the truck has been cleared start at the trailer's 7-way connector and make sure it's clean and free of any corrosion. Then trace the wiring back to the lights looking for any pinches or damage. Also check the ground locations. They should be attached to a clean, bare metal surface.

If you still can't solve the problem, let me know what you've found, and we'll keep troubleshooting.

expert reply by: Charles S