1998 Chevy Silverado

Hello and thanks for donating

most likely culprit for inoperative tachometer would be faulty instrument cluster. Need to disconnect the instrument cluster wiring connector and also the ignition coil connector. Connect a test light between the cluster connector terminal #6 (white wire) and ground. If the test light does not illuminate then further testing is needed. If test light illuminates then there is a short to ground needing repaired in the white wire between instrument cluster and ignition coil. So if the light did not illuminate, you'll need to connect the test between terminal 6 again and this time terminal "B" (white wire) of the ignition coil connector. If the test light illuminates here then the instrument cluster needs replaced. If the light does not illuminate then there is an open in the white wire between cluster and ignition coil that needs replaced.

Oh okay, probably was just a wire left loose from the alternator then. There should be a white wire running from the instrument cluster to the altnerator, this wire was most likely left off or not tightened up properly during replacement of the alternator.