Q: How to troubleshoot the brake light switch for GMC Sierra and GMC Yukon?
A: The brake light switch is on the side of the brake pedal and is activated when the pedal is depressed. If the brake lights are not working, check the fuse and then check for voltage to the switch on the feed wire. If voltage is present, depress the brake pedal and check for voltage at the output wire terminal. The installation is reverse the removal procedure and ensure the retaining clip is properly installed.