Did You Check All The Connections On The Guage Cluster And Then Check The Main Harness Connector Near The Hood Hinges...the Harnesses Are Known To Crack/break Wires Inside The Harness -- Wire Plastic Casing Gets Old And Cracks And Then The Wires Break. If That Is Okay, May Have To Look At The Connections At The Coil Etc. If Thats All Okay, May Have A Fautly Tach.... Did You Try Another Tach Yet??