Troubleshooting Trailer Running Circuit that Works with Only Other Vehicle and Other Trailers

Question:

I have a brand new kayak trailer with led lights. I installed C56106 on my 2011 Toyota Sienna. I have turn signals and brakes but no running lights. When I attach the trailer to another vehicle everything works perfectly. I have tested this on a secondary vehicle multiple times and the trailer works perfectly. The fuse on part C56106 is not blown. I have ensured the ground is connected well as instructed in the installation video. When I plug in a 4 pin tester on the 4 pin connection on the tow vehicle the tail light lights up. This suggests that I am getting power just fine. Of course all the other functions check out properly on the tester as well. It seems as though I have enough power for the tester but when I attach the trailer I don’t have enough power for the lights. Any ideas?

asked by: Jeff

Expert Reply:

This is a really odd situation but it sounds like the trailer just doesn't have quite sufficient enough of a ground to power the running lights. So what I would try is running a jumper wire from the ground wire of the light assemblies to the main ground harness to see if improving the ground helps. Typically this is all that it takes.

I attached a couple help article links on trailer wiring troubleshooting for you to check out as well.

expert reply by: Jameson C