Assuming the other gauges are still working(?) you can expect the problem is not fuse related. I have no idea how much fun it will be, but the starting point for me would be the fuel sender wire at the tank. I would suggest removing the wire, watching the gauge and "flashing" the wire to ground somehow. If the gauge responds, the gauge and wiring are PROBABLY working and the sender in that tank would be suspect.
Again, I have no idea how accessible that unit is on your tractor.
