Free Access to Car Alarm/Keyless/Remote Start Wiring Diagrams
the12volt Good Resource, lots of specific questions and a great place to post any specific questions. Not the best wiring database
Modified Life Decent Resource like 12volt, Not quite as comprehensive.
Commando Car Alarms Wiring diagram resource with so so diagrams, nice basics on main page, bottom left side.
And the reason for this post:
BEST WIRING DIAGRAMS Awesome wiring resource, found this through a backdoor (let's hope it stays live). Almost as good as the professional installer site: directechs (of course you need a dealer account to use!) This site has installation notes, and even attachments for situational wiring such as relays for specific vehicles.
Hope this helps, back to work for me! (P.S. Nissans are a bitch, I still haven't taken my christmas lights down, lol)