Greetings:
To increase everybody's base line knowledge AND decrease smart ass remarks from a few people who think they know it all: could I suggest the following reading?

Bentley Volvo manual, of course

Haynes manual as back up in case Bentley seems too complex.

Bosch Automotive Handbook circa 1995 or so edition.
Robert Bosch Auto Electric-Electronic Systems - red book circa 1988-1995
AND, THE SIMPLEST BASIC BOOK that isn't child like. The Bosch Book of Motor Cars, by John Day. Bosch books are technically accurate, easy to understand, have excellent production qualities and fonts, and are often durable. We need the older versions if there is a choice, as the latest Automotive Handbook will discuss NEW 2010 STUFF, WHEREAS a 1995 version will focus on LH injection, halogen - not HID - lights, etc.
Amazon have sold me all except the Bentley manual for about $15 each delivered, although the price goes up and down, as used bookstores sell through Amazon. All my copies have been in good shape and promptly delivered.
Reading this material reinforces the understanding of the wiser Brickboard members and their product specific advice.