Troubleshooting Trailer Running Light Circuit Not Functioning on One Side of Trailer

Question:

I have a 7 prong trailer plug on my truck with a reducer pigtail down to a 4 prong plug on the trailer the problem is that I dont have running lights on the right side everything else is working 4 ways brake lights turn signals I pulled the back of my plug apart on the truck side and out of 7 prongs I have 4 that work I checked it with the running lights and 4 way flashers on at the same time 2 prongs flash and the other 2 are steady light on my test light the center prong would be the ground I presume what are the other 2 prongs?

asked by: Steven T

Expert Reply:

Since your running light issue is only on one side of the trailer that indicates that the issue is on the trailer wiring. Most likely you have an insufficient ground on the light assemblies on that side of the trailer. If you can fix/improve the ground on that side of the trailer you will fix the issue you are having. A lot of trailer lighting assemblies ground through the mounting hardware of the light so make sure your lights are mounted to a clean metal surface. You can also run jumper wires from the brackets back to the main ground wire as well.

expert reply by: Jameson C