I just bought my son a 1986 IROC Camaro. We have the center high mount stop light, but it is not attached. I'd like to get a schematic for this system and/or a good explanation of how it works. It appears it is associated with the rear window defogger and rear hatch motor(which runs continuously when attached). Thanks in advance for you input.

 

The 3rd brake light and demister are separate circuits, although are physically proximate of course.

No mystery to the operation - the brake switch 12v signal goes via it's own wire through the black contact block next to the hatch motor, and up to the brake light via braided wiring bonded to the glass. The ground return goes back through the contact block, and shares a ground on the beaver panel with the hatch motor.