Troubleshooting Horse Trailer Lights That All Suddenly Stopped Working

Question:

Why would my lights just all quit working on my horse trailer. I didn’t blow a fuse. What else could

asked by: Chasey

Expert Reply:

The best way to troubleshoot your trailer lighting problem is to unplug the trailer from the tow vehicle and test each one individually.

If you have a circuit tester like # PTW2993 you can test the vehicle connector to make sure the lighting signals are reaching it. If not, then you know you need to check all fuses and relays related to towing and to inspect the wiring and connectors for signs of corrosion or a loose ground wire.

When all lights suddenly go out at the same time this could be caused by a loose ground since this would affect all lights at once. Find the main wiring ground wire and make sure it is tightly attached to a clean bare metal surface that is free of paint, primer, undercoating, grease, rust, etc.

The trailer can be tested with a spare battery or the one in the tow vehicle. Use some wire to apply power directly from the battery to the trailer connector contacts. Connect the negative terminal to the ground pin on the trailer and then one by one apply +12V power to each of the circuit pins. This will let you know if the trailer lights function without involving the vehicle's wiring. If the lights do not work when fed direct power, then check the main ground wire on the trailer and in the same way make sure it is tightly attached to a clean bare metal surface.

Dielectric grease like # 11755 can help protect electrical connections by blocking entry of water and other contaminants that can cause corrosion.

expert reply by: Adam R