I will assume that the brake issue is when backing up and that they did work properly at some point in the past. Is this the same tow vehicle as when the brakes worked properly? The reverse solinoid is activated by the backup light circut. If you have a 5pin flat plug you can reverse it leaving the ground hanging out, turn on the tow vehicles running lights and that should activate the solenoid. Try backing up. If all is good then you know ,in the proper configuration of the plug, you are not getting juice to the trailer plug. The problem will be in the tow vehicle plug. Fuse could be blown or wiring needs to be looked at.This is a Ford wiring diagram for the 7 way. Either way the blue wire is the on to look at to make sure there is power when in reverse.Pretty simple…I probably made it more complicated than it actually isBob