How to Add Factory-Style Fog Lights to a 2005 GMC Sierra 1500 uberant.com

Run a fused power wire from the positive battery terminal to pin 30 on a standard automotive relay. Ground pin 85 to a clean chassis ground. 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 low beams to be on. Use heat shrink tubing on all connections and zip-tie the harness away from hot or moving parts.