dumb wiring question

ok I have a 2002 sierra and I hooked up my trailer, I used the wire adaptor to go from the 7 pin to the 4 pin, everything works but when I press the brake pedal the trailer lights go out.. I have replaced all the wiring on the trailer, and it still does it,, anyone have an idea

Sounds like you have managed to put your lights in "series" with each other. Make sure your lighting circuits are "parallel".