[ronk49753]

Dweebs write firmware for brake controllers. My Bully forever flashes a constant *E3 error code which in the manual says that the trailer brake solenoid circuit is open. Of course it's open you idiot programmer, the trailer is not connected to the truck!!!! The thing works great when a trailer is connected tho.
Yes - the controller needs to know when you step on the brake pedal, once that wire goes to 12V, then the controllers motion sensor will sense how fast the truck is slowing down and apply the correct amount of voltage to the trailer brake solenoid circuit which applies the trailer brakes from a low voltage "soft" stop or a 12V "panic" stop. The controllers manual slide bypases the brake on wire and the motion sensor and simply panic stops the trailer.
If you have access to a voltmeter, test each wire on the back of the controller & see if one of them goes to 12V when you press on the brake pedal. If none go to 12V then you have a problem in the truck wiring or switches (I am assuming that the brake lights in the truck work OK). If one does go to 12V, then the problem is in the controller. It may well simply be that you have the gain turned down too far (hopefully). The gain control is a potentiometer and the contacts inside are therefore subject to corrosion if not moved very much. Sweeping the gain knob back and forth several times will usually clean up the contacts.
Hope this helps