Bulldog Security no longer works :(
Install Doctor also doesnt carry accurate information. I looked at the GM info which doesnt mention 2001+ changes and Mazda which doesnt mention 1999-2001+ changes. This is okay if you have the older cars like me but it's not very helpful if you have the newer models or if you have an older model and are trying to blend some of the newer OE parts in. :/
There is allso ALLDATA which costs $15/yr per vehicle but will give you ALL the information you could ever want on your car, both mechanical and electrical. It offers connection pinouts and wiring color codes for every harness and section of the electrical system. Truely invaluable to us who are looking to integrate more than just the sound system. Especially for such things as the BMW I-bus or similar systems like that offered in 2001+ GM vehicles.
Its kinda expensive but what may be possible is for us all to use a unified account and each pay for our specific vehicles -- thus expanding the SHARED knowledge between differant models and years... not sure how well it'd work but just an idea.