my speedometer and rpm and gas gauge nt workin ,why?

perhaps the chassis ground isn't seein' much ground~ take off the bolt that holds the big 1/0 negative battery cable onto the frame/chassis and wirebrush the lug and the spot where it bolts to, to insure a solid 300 Cold Cranking Amps potential...there is also a 1/0 cable that goes to the motor block...these should be clean electrical connections...also assure the battery is NEWer than five years old~