The five red running lights across the top rear of my TT are not working. The ones on the sides and on the front work OK. I want to hook up a backup camera but the power feeds from these lights. The TT is a 2020 Ameri-lite 257RB.
If you have cabinets in the upper rear of your trailer, you may get lucky and be able to pull a panel in there to access the wiring for those lights. Depends on the trailer, but I've done this many times.
I found the problem. I pulled off all the lights on the back where I could see and test the wiring. The "hot" wire to the running lights was OK, but the ground wire was not connected to anything! (great build quality GS!) Hooked up a short ground wire and all lights are working now.