Troubleshooting Marker Lamps on Trailer

Updated 02/10/2021 | Published 02/08/2021

Question:

Hello. I was need some help from one of y’all experts. I have trailer that I added some led side markers to. After I added them and wired them up only my rear trailer lights work the side markers don’t but if I disconnect the rear trailer lights the side marker work. I’ve cleaned all the ground even ram a new brown wire to the rear. Any suggestions?

asked by: Janson D

Expert Reply:

I'm suspecting a bad ground connection somewhere. Usually when something strange like what you describe, it's the result of a poor ground.

How did you wire the side markers? Those would usually be installed inline with the running lamp circuit as it runs down the side of the trailer. Assuming the running lamp circuit runs down one side of the trailer, you'd tap the running lamp into the circuit and for the running lamp on the other side, the easiest way to connect that is to daisy chain it into the running lamp circuit of the closest taillight. The running lamp would either ground through its mounting hardware being in direct connection to the trailer frame or via a ground wire attached directly to the trailer frame. Does the trailer have a tilting tongue or bed? If so, you might need to use a jumper wire to tie the tilting and stationary potion of the trailer together for a continuous ground circuit.

I'll link to some trailer wiring help articles that you might find helpful.

expert reply by: Mike L