hooked up my 7pin connector from my trailer to my 05 2500. while checking the lights I noticed the brake lights do not work. with headlights on the avalanche all the running lights on the trailer work. press brake pedal all lights on trailer go off and no brake lights the trailer. have not hooked this trailer up in several months. getting dark and started to rain so I called it a day. have not checked anything so far. any ideas where to start trouble shooting?