Troubleshooting Trailer Brake Lights Not Working with One Vehicle But Work with Another

Question:

I installed the curt 56299 wiring harness on my 2016 Honda accord a couple years ago for a small trailer. recently i purchased a old boat and trailer, rewired the trailer withe new wiring harness. when i connect the car to the trailer, i have turn signals and lights but no brake lights. when I hook it up to my Buddys truck everything works on the trailer. we are Baffled.

asked by: Scott W

Expert Reply:

Most likely the trailer has a weak ground and if you improve the grounding of the main trailer wiring harness and the grounds of each of the assemblies you'll see them start to work like normal. The brake lights draw the most amperage of all of the circuits so if there's a weak ground and the tow vehicle doesn't have a lot of amperage the circuit may not work.

I also attached a help article on trailer wiring for you to check out as well.

expert reply by: Jameson C