1999 Jeep Grand Cherokee

You would first need to find out if the gauge is getting a signal. You might do a quick check on a scanner to see if you have a tach signal there in the live data. If you do then you can reasonably assume a signal is being sent from the module or distributor (I’m not sure where the tach signal comes from on that vehicle). If you don’t then perhaps the problem is where the signal is generated and not at the tach itself.