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

Begin by connecting the positive leads to the battery positive terminal. Secure them firmly, ensuring the fuses are installed in their holders. Next, connect the ground leads to your prepared chassis ground points. Use a 10mm bolt and nut to secure them tightly to bare metal—a poor ground negates all benefits of the harness.