Not sure of your setup, but try to divide the problem between the Dash (or underdash) electric brake controller and the electric brakes themselves. Obviously, the electric brake rear bumper plug is in. Do the trailer brake lights come on at brake pedal depression? I'm assuming the electric brakes you have are individual solenoids placed inside each brake drum/shoe assembly. If they are, you can have someone operate the brake controller manually. Walking around each wheel, you should hear a "buzz" as the 12 vdc energizes each solenoid. It's not that uncommon for the solenoid wires to actually rub (and chaffe) on any brake component (especially the drums). If so the controller should report an "O.C" type of code upon actuation, the of course you lose braking. If you're still having problems, mention the type of system you have, I could always attach a "typical" schematic.
