Troubleshooting Trailer Lights That Dont Work When Running Lights Are On

Updated 05/03/2018 | Published 05/02/2018

Question:

Brake, turn signal and emergency flashers all work. As soon as running lights turn on nothing works. Already fixed ground wires running to the frame. This is on an ice castle fish house. Do I have wires crossed. Bad wire somewhere? I hook my truck up to two other trailers and lights work fine.

asked by: Jeff

Expert Reply:

The wiring issue may be on the truck side, but is definitely a ground wire issue. Make sure your ground wires are bare metal to metal and free of corrosion or debris. Once they are secured, you can add dielectric grease or paint to keep corrosion away. The running lights pull a lot of power, so with a weak ground, the functions don't work once that power draw kicks in. Make sure you check the ground connections at the main ground as well as at the tail lights as these are often grounded through the mounting hardware.

The ground issue could be on your trailer, but it is also possible for it to be on your truck itself. Just because your truck can power the other trailers doesn't mean that the larger power draw on this trailer may not be effected by a truck ground wire issue. Make sure you check the ground wire on your trailer connector and make sure it is bare metal to metal. You can double check the connections using a circuit tester like # PTW2993 to make sure you have a good ground at your trailer and your truck in all those locations.

expert reply by: Jason S