Dear mb300d,If you've already replaced the sending unit,the only other thing left is the wiring. I would check the power to the gauge itself, by pulling out the cluster and using either a volt meter, or a test light to ensure you have juice. After that, maybe disconnect the wire that runs to the sending unit, and temporarilly run a jumper wire, outside and seperate from the car's wiring harness. If the tach works now, you'll know that the factory wire is no good.