1985 pontiac grand am. speedometer is pegged to 100mph at all times. Any ideas?

Sounds like a broken or seized speedometer cable. This will require disassembling the dash to get at it. The cable is not an expensive part but the labor involved is usually fairly time-consuming.

the whole instrument cluster comes out in one piece I have a 85' and it's electric no cable ...so i think maybe pull it out maybe clean the connections or look for a relay ,fuse.,Also you could just find another cluster at a salvage yard ..