Trailor Brakes dont work

I own a 2002 Chevrolet Silverado 2500 HD Duramax Diesel. The trailor brake quit working. I checked all the fuses several times and none of them were blown. I can get the trailor brake to work if I use if manually, but I will not work when you st ep on the brake pedal. I took the trailor brake out of my suburban an installed it into the duraman and the problem still exists. All the brake lights on the truck and trailor work when I hit the brake pedal but the trailor brake will not engage. On the wire harness for the trailor brake there is a wiring diagram. One of the wires said input from vehicle brake light switch. I checked the voltage on that line and there was 0 volts wether you step on the brake pedal or not.

Do you think the brake light switch has gone bad?

There are several wires comming off of the switch. Is it possible that one goes directly to the brake lights, and one of the others go to the brake controller. This could explain why the brake lights come on when I step on the pedal but no output from the brake controller.

Signed
Please Help!