I bought a trailer new about six years ago. The first year I had a couple of trailer light problems and fixed both after trouble shooting. Literally every time I use the trailer there is a light (brake) or running light problem. Finally, I had enough and am replacing the entire wiring harness.
I found 42 mechanical connections (crimp) in the factory harness none of which was properly supported nor had dielectric grease to manage corrosion.
My installation will have zero no mechanical crimp connections (wrapped and soldered), all sealed with dielectric grease and shrink tubing. I've cut my connection down to 14.
Just a shameful factory design.
Tell me and I forget. Teach me and I remember. Involve me and I learn.