Where can you find a diagram for a fuse block on a 1990 Pontiac Firebird?

This information can be found in your owner's manual. If you do not have one, then I suggest you get one. You need an owner's manual to know what items to service and when, and for specifications. You can order one from a dealer, find one at a salvage yard, ebay, or one of these sites: http://www.carownermanual.com/ http://vehicleownersmanual.com/ http://www.vintage-books.com/owncat.htm