Trailer Brakes Locking up on my new truck?

I have a 20' flatbed equipment hauler. It has a 6-way metal plug on it and, it works fine with my 2005 chevy 2500hd. I bought a new 2010 ford f250 4x4 put a new brake controler in it and a 6-way to 7-way adapter plug and now as soon as i hook up the trailer to the ford and move 5' the trailer brakes lock up completly. Also, thats without touching the brake pedal at all. I also have a dumpster trailer that my new truck and adapter works fine on so its gotta be the trailer right?

just some ideas plz