heated seat wiring?

Does anyone have a wiring diagram for the heated seat? and where is the relay for it?

I don't know for your year but I highly recommend the Factory Service Manuals.
Do a search on this site for Shop Manuals and you'll find some references as to where you can get the Original Factory Manuals.
Also, go to Ebay motors and search Manuals and you'll find what you need. The FSM set consists of 2 volumes for your car, very complete technical information and all wiring diagrams for your year vehicle. Ebay is usually less expensive than the original publisher, Helms,inc.
Ebay link to Buick Manuals
http://cgi.ebay.com/ebaymotors/Parts-Accessories_Manuals-Literature__1995-Buick-Riviera-Service-Manual-GM-Riv-95_W0QQitemZ260313451087QQddnZPartsQ20Q26Q20AccessoriesQQadiZ2872QQddiZ2811QQadnZManualsQ20Q26Q20LiteratureQQcmdZViewItemQQptZMotors_Manuals_Literature?hash=item260313451087&_trksid=p4506.c0.m245&_trkparms=72%3A543%7C65%3A12%7C39%3A1%7C240%3A1318

I just looked a little closer at this set and they are well used used, you can search further and find a new or newer set.