1993 Jeep Grand Cherokee gas gauge reads empty but tank is full.

Sounds like your sending unit could be bad.

It has to be the float, may need recalabrated

Doubt it.
The same fuse for the gauge would handle the rest of the cluster.
Probably the sending unit in the tank.

sounds like module went out. it's in the tank

Check the Fuel Sending Unit in the fuel pump. Disconnect the wire to the sending unit, at the tank, and ground it to the car frame. Turn the key to on and see if the fuel gauge goes to Full. If it does the gauge and wire are good and the problem is in the sending unit. If it's still on E the gauge is bad or the wire is open.

Keep us updated.

COULD BE FAULTY FUEL SENDING UNIT IN FUEL TANK ON THE FUEL PUMP ASSEMBLY.

Disconnect and replace fuel filter.With filter disconnected have someone momentarily turn key to on position to see is fuel pump is working.Make sure you have lots of rags,a drain pan and safety goggles on

There could be two problems here:
1. That buoy floating tank is not working properly
2. That the electrical system that fails to submit the dashboard.

Review this information:
- ZJ-Secc-8E-Instrument-Cluster-and-Gauges
Page 2 - Fuel Gauges description
Page 4 - Voltimeter/Tachometer/Fuel Gauge/Low Fuel Inoperative
Page 10 - Specifications
- ZJ-Secc-14-Fuel-System
About Fuel Tank components
- ZJ-Secc-8W-Wiring-Diagrams
Fuel Tank and Gauge & Sensor Units Sending (Page 93 and next)

Good luck... and remember rated this help.

by myself

There is a sending unit in the fuel tank that registers how much fuel there is. It is probably broken, giving you a funny reading on your gauge.