Adding Factory-Style Fog Lights to a 2000 GMC Sierra daddycow.com

Run a fused power wire from the positive battery terminal to pin 30 on a standard automotive relay. Ground pin 85 to the chassis. Connect the trigger wire from the headlight low-beam circuit to pin 86. Finally, run a wire from pin 87 to the positive leads of both fog lights. Ground the negative leads of the lights to a clean metal surface near each light. Inside the cab, install the dedicated fog light switch in a blank dash panel. This switch interrupts the trigger wire from the headlight circuit, giving you manual control while still requiring the headlight to be on.