you have a serios wirring problem if live near sac i'd be willing to help you. You have current being applied after the brake switch and combo switch . the only connector that those two circuits share is c216 pin cavity 3 and 8 (underhood fuse box) if they were crossed here nothing would happin since it is the switch when turned on allows the current to travel. look at this picture this is connector c418 it is the turn signal circuit look for a grn/wht wire out of place (grn/wht is the brake circuit) between pins 15-17. hope this helps