I'm pretty sure it's Operator Error, but just in case I'm asking for help. I renovated the utility trailer I had that used to be a Venture popup camper but was just four short walls on a frame when I got it. The walls more or less collapsed from exposure to the weather, so I stripped it down to the frame and wire-wheeled the rust off, and painted it with rust reformer and primer. No problem there. I rebuilt a nice sturdy frame with 2x3s and clad it on the outside in a temporary way with luan, still open on the inside. I got a new wire package for the lights and followed all the directions, used wire nuts and electrical tape after that to seal all the connections. It went as smooth as I've ever seen, but once I hooked it up to the car--nothing. I checked and moved the ground connection to a more naked metal part of the frame. Nothing.
How can I find out what's wrong?? What I actually did for the ground was use an old ground wire that was still connected to the frame, stripped off a 1/2" of the end and connected it to the ground wire of my harness. It's a 4 wire basic harness.
The answer to this problem was so dumb!! I had built the trailer walls from wood, and the lights at the back had no metal touching them at all, so no matter what I did, it wasn't getting any ground. I rewired both sides with a definite connection at one of the sidelights to a grounded area and it worked like a charm. Sheesh!