My rear brake lights are not working. They light up low when I turn on the on the headlights, but they don't light up brightly whenever I step on the brakes. I've checked the bulbs. All are good. I've checked the fuses in the driver's side kick panel. They appear to be good also. Any other suggestions?

 

check the switch at the brake pedal.

I am assuming this is a S5 (89-91) as there is a burnt brake light indicator on the S4 models, which would rule out everything after the CPU

 

This is on an S4 actually. '88 GTU to be exact.

 

If none of the bulbs light up and there's no warning light when you push the brake pedal, it's most likely the switch.