Narrowing down trailer light problem

It sounds more like you have a bad ground somewhere.

 

you have a flaky ground, start theres junction box where it all comes together, thats the place to start

 

Wrap electric tape or a 2" wide vinyl tape around the nose pigtail receptacle. This will help prevent insulation getting rubbed and wires getting pinched when you install.

It does sound like a ground. It also could be a bad light.
Good luck

 

Get a rubber hamer and tap on lights with everything on and watch for changes in bulb brightness, you may find a bad shorted out china made light that was replaced on road one night?

 

Pull all the lights out from the right rear housing, you may find a bad wire in that region.
I pulled a Wilson grain trailer, it was a real mess in there.
Recently with my Doepker trailer I had a short, blew the fuse, in my clearance lights, turned out to be in the license plate light socket.
Your problem will be where ever it is that the marker lights and the right tail lights all meet up.

 

Yea you would think so, but not. Very surprising that more trailers do not burn to the ground. Clean everything, a good electrical contact cleaner will help if its colorful, and things are growing, make sure the ground lug is clean, sand or wire brush. Good luck had to go in there plenty of times, never fun.

 

Pigtail box
Belly lines
behind the left side brake lights.

I've found an ABS light that was grounding out where the wires came out of the box behind the brake lights. Some times it can be the most minute thing that causes hours of grief.

 

Glad you found it.