Any suggestions for troubleshooting?

 

The circuit for the tachometer on the gauge cluster is the ignition coil, the wiring, then the gauge in your cluster. A problem with any of these items will cause the gauge to not work. I'd start with the simplest and check the electrical connection to the ignition coil for any corrosion/poor connection.

The next step would be if you have a volt meter that can read hertz (Hz) or possible in ac voltage mode to see if the meter can pick up the signal in the wiring.

You could also pull the cluster to see if you have a poor connection or cracked solder joints on the circuit board for the tachometer.