Check your ground wires. A weak or bad ground is often the problem. I just hook the brakes directly to a 12V battery to see if there is connection. There is no polarity on electric brakes, so you can't hook them up "backwards". One wire goes to the 12V source, the other to ground.
eTrailer has good info on wiring.
eTrailer wiring diagrams
Me, Julie, Lil' Barry, Faith, and OSDs, Fang and Treaty
2003 Hyundai Starex (H1), 2012 Coachmen Clipper 126
I don't know when we'll be able to go camping again...