How to Install a Headlight Relay Harness in Your 2005 GMC Sierra 1500 daddycow.com

With the relay harness connected, plug your headlight bulbs into the new weatherproof connectors provided by the harness. These are clearly labeled—typically "LOW" and "HIGH" for each side. Double-check all connections are fully seated and secure. Reconnect the negative battery terminal. Before reinstalling the headlight assemblies, test all functions. Turn on your parking lights, low beams, high beams, and flash-to-pass. Verify everything works correctly. If you experience flickering or non-function, double-check your ground connections and ensure the relays are fully seated in their sockets. The BCM (Body Control Module) in your Sierra monitors many electrical functions, but a quality relay harness should not trigger any errors .