I'm an electrician and still get pissed when I have to trouble shoot and repair my boat trailer lights (almost yearly). I finally had enough and in 2019 I re-wired my trailer from scratch. All my connections are twisted, soldered and sealed in heat shrink, I installed new LED lights, and used abrasion sleeves where the wiring harness came in contact with the trailer frame. I got so tired of replacing the crappy #12AWG jumper wire on the hinge of my folding tongue - I replaced it with a 10" long x 1" wide copper braided grounding strap (I think this bad boy is rated for 320A) and used 1/4 x 20 bolts to secure it!
I also keep those remote lights from Princess Auto in my truck as a back up and find they work well in a pinch (as long as you have a good supply of 'C' batteries). When using these always use a small wire and lash them to the trailer frame so that you do not loose one on a bump.
