The one Gavin recommended should be right for your car. If the one you bought is the same (and doesn't just "look" the same) and has the same part number then you should be able to plug'n'play.
Don't try and decipher the wiring using Haynes, their diagrams are a nightmare at the best of times! Try this instead, starts on Pg55 by document reader page number :
http://www.myvolvolibrary.info/Tech_...ction-3-39.pdf
There's about 4 different variations depending on 4 or 5 door and other things, make sure you get the right one for your car!