After Adding More Lights to a Trailer the New Lights Will Not Work

Question:

Hello, I have a 16 foot car hauler trailer and am using it to haul hosue hold goods. I enclosed the trailer and want to add an extra set of tail lights. The lights on the trailer and the extra set I bought are the 2wire type that you plug in to the back. After splicing into the existing wires and running them to the new lights, I cant get either one to work now. What did I do wrong?

asked by: Mike

Expert Reply:

There are a few possibilities. First, and easiest to correct is maybe the wires you spliced into were not the right ones. By that I mean that there isn't exactly a standard for trailer wire color and function so unless you tested the wires first with a circuit tester such as # PTW2993 or a meter it is possible that the wrong wires are connected to the wrong circuits.

This would be easy to determine as long as the lights are properly grounded. But if they are not then the circuit cannot be completed and the lights will not power on. On new taillights and wiring harnesses the white wire is the ground. So, we have the possibility that something was mis-wired and the possibility that the ground connection is not made or is not attached to a clean bare metal surface.

Third, if all of the lights are incandescent then the additional lights could overload the system which can result in either the lights not working or it could blow a tow package fuse on the tow vehicle. If you disconnect the other lights and the new ones start working then that is likely the issue. Switching everything to LED lights would solve that issue. I have included some links that should also help.

expert reply by: Michael H