Q: How to diagnose and replace the brake light switch on Chevrolet Colorado and GMC Canyon?
A: The brake light switch activates the brake lights when the pedal is depressed. To access the switch, the under-dash panel and the heater/air conditioning duct need to be removed. If voltage is present, check the brake light wires at the tail light housings for power with the brake pedal depressed. If there is no voltage, repair the circuit between the switch and the brake lights. If voltage is present, check for bad ground by using a jumper wire connected to good ground and probing the ground wire terminal at the tail light connector.