It really depends on what depth of information you are looking for.
has wiring diagrams for most cars,
you could also check out www.the12volt.com
they may even have discusions on the alarm you are looking at getting. I have one more link at home and will try to post that later tonight.
I feel that chilton is worthless in this regard, because it has one page that just shows the wiring interconnection, and not "here is a picture of your kick panel, and this pink wire here is what you need".
As for shop manuals, i have yet to get one for my car, or ever see one, so i do not know what type of documentation those have.
What exact brand/model are you getting, i am almost done with the research portion of my own 2 way paging alarm system, and may be able to lessen your research.
Also if you are looking to buy a shop manual, i found a great site with discounted prices, again the link is at home and i will post it if you request it.