Some places to find commonly used wiring diagrams for GM vehicles include HelmInc.com and AutoZone.com. GM also makes owner's manuals, including wiring diagrams, available on its website.
At HelmInc.com, users can search for wiring diagrams by GM, and then by model and year. At AutoZone.com, users can find a complete wiring guide for GM trucks made from 1988 through 1998 in PDF form. At the official GM website, users can search for owner's manuals based on brand. Some of the available brands include Chevrolet, GMC, Pontiac and Saturn. Additional brands include Cadillac, Hummer, Oldsmobile and Buick. The earliest manuals offered date back to 1993 for Pontiac and Oldsmobile, while current ones are available for Chevrolet, Cadillac, Buick and GMC as of 2015.