Take the sill panel off and pull up the mat on the driver's side along the seat area and up the driver's side between the back of the door and the driver's side of the rear window. The wiring goes along this area, and sometimes corrodes and shorts out in behind the seat and along the bottom of the door sill area.
The wire you are looking for is a lightgreen wire. It comes right off the brake light switch on the pedal arm. It splits and goes to the steering column and straight up to your rear brake light. It also splits off and goes to the cruise system if you have that.