I towed my equipment trailer (empty) this morning to the job so I can p/u my skid steer.
This afternoon when I loaded up and began driving I didnt have electric brakes. Everything else worked on the trailer. Called my brother to help me figure it out and funny thing was when he put his foot on the trailer tongue to tie his shoe the it registered that I had a connection when he took his foot off I had no connection. (I have a Prodigy controller)

I went back and kicked the tongue area of the trailer and had my brakes back. (registered positive on the controller) Had brakes all the way home.

Question... the black box on the trailer where the safety brake cable connects, anything I should look at there?
Anything else I should look at?

You may have a bad connection on the ground wire on trailer.
When you kicked trailer, a ground was made from trailer through the ball/hitch, to the truck.

PM trailerpro, he probably can help.

need to check your ground wire. The trailer is trying to ground through the ball and hitch. Watch your marker lights to see if they flicker. Also, sometimes, the blinkers will ground back through the marker lights and make them flash.

You found your own problem and didn't even know it. It is the ground, and it's grounding through the ball. I think that is 3 votes for ground.