Troubleshooting Trailer Brake Lights Not Working with New Light Assemblies

Question:

trailer brakes lights dont go on Brought a new set of trailer brake lights old ones didnt work but when I apply the brakes they dont go on

asked by: Gil L

Expert Reply:

It sounds like your lights weren't the issue and most likely you have a wiring problem. To begin troubleshooting, I recommend disconnecting your trailer and using a circuit tester like # PTW2993 to first test each function on your vehicle side wiring. I've attached a video to assist. If you don't have that function, the issue is on the vehicle side wiring, and you most likely need to replace a fuse or the harness itself.

If you have the trailer wiring working correctly on your vehicle, then I recommend connecting your trailer and then checking the wiring functions at each tail light. If you don't have the function there, then trace that brake/turn wire probing every few feet to find the short. If you have the function at your tail light, then the ground is an issue. Make sure the ground, which is often through the mounting hardware is bare metal to metal and free of any corrosion or debris. If you have the separate white ground wire on your lights, then make sure it is grounded to your trailer frame bare metal to metal.

I've attached a couple articles to further assist.

expert reply by: Jason S