http://www.webring.org/cgi-bin/webring?ring=clubjbody;list

This is a Cavalier (same car) webring, one of the links might show some owners installing other stereos, and where they ran their power wire. I'll bet one of them will show it. Also - if you can find a bulletin board for the car, it's likely to be in an FAQ or there will be an old post asking about it.

http://www.j-body.org/

This one looked pretty good too.

Happy browsing!