I recently installed a remote start/alarm system into my S70, some pictures of the install can be found here:
http://www.flickr.com/photos/wesgill/

Thanks to a good friend, I was able to get these sheets with wiring information for the S70. I also snagged some audio information since I'm planning on building my system in the coming months. The sheets were very helpful to me and hopefully will be helpful to others looking to do some work on their cars.

http://www.wesgill.net/files/volvo/v...video_base.jpg
http://www.wesgill.net/files/volvo/v...y_with_amp.jpg
http://www.wesgill.net/files/volvo/volvo_s70_wiring_audio_video_early_with_amp_2.jpg
http://www.wesgill.net/files/volvo/v...e_with_amp.jpg
http://www.wesgill.net/files/volvo/v...with_amp_2.jpg
http://www.wesgill.net/files/volvo/v...t_security.jpg
http://www.wesgill.net/files/volvo/v...security_2.jpg
http://www.wesgill.net/files/volvo/v...security_3.jpg