2007 Silverado 3500 dmax Trying to figure out what's wrong with the integrated brake controller on my tow rig. I disconnected the trailer and Tested the circuit with a 12v light and still get "service trailer brake system" on the dash. I really don't have time to drop it off at the dealer. Does anyone know what's up? How much is there to the system? I understand there is a interface ( on the dash) and a module. Is that right. Thinking of replacing it all or should I just make time for the dealer?