How to Install a Headlight Relay Harness in Your 2004 GMC Sierra 1500 morsunled.wordpress.com

Use zip ties to secure the relay harness along the radiator support or inner fender, keeping the wires away from moving engine components, exhaust manifolds, and the fan shroud. Ensure the wires are not rubbing against any sharp metal edges. Reconnect the battery negative terminal. Turn on your headlights and verify that both low beams and high beams function correctly. If one side does not work, double-check that the trigger connectors are fully seated—they can feel connected when they are not locked in place.