Frank,
The temperature gauge and the fuel gauge both get power from the instrument voltage regulator (~10 volts). The circuit goes from the IVR, through the fuel gauge (which is really a current meter) to the fuel gauge sender (which is a variable resistor) and then to ground.
Since your temperature gauge works, the IVR appears to be supplying power (maybe not the right voltage, but at least it is not dead). You can use a voltmeter to see if there is about 10 volts getting to the fuel gauge terminals.
A bad connection anywhere in the circuit will stop the current flow and make the guage stay on empty. The only difference between the fuel gauge and the temp gauge is the markings on the face; you can swap the wires from the fuel gauge and temp gauge to see if the fuel gauge is working. The fuel gauge sender should measure about 33 ohms in the full position and 240 ohms in the empty position.
I would bet that you have a bad connection, a broken wire or a bad ground at the sender.
Have a good trip to Ireland!