I recommend you get a repair manual if your going to work on your Volvo. It's real easy now that they're available online. To be better prepared when working on your vehicle, read up on the job you're about to perform. They'll show you a step by step instructions for the alternator replacement on the S80 engine.
Try http://bit.ly/mitchell_repair_manuals_online and you can have one in minutes, for less than $30.00.