7 Pin Truck Trailer Plug. All other features (turn, stop etc) work. It will be sticking out and taped up up with electrical tape.
There is a lot wiring that you have to tie into your truck's wiring harness, but it is easier to do than it seems. Note that although the colors and wire sizes listed herein are common, they are not. After all my years pulling trailers, etc; and seeing the way lighting reacts when not being properly grounded, I would lay long odds that was the problem.
I tried looking for a fuse, but nothing in the manual jumps out that says trailer battery power.
Mine is hot all the time which seems odd to me.
Brass pins in a durable housing. construction prevents rusting, enhances appearance and makes. All other features (turn, stop etc) work. I'm thinking of picking up the above mentioned parts as well as the factory trailer brake controler.