Temperature Gauge Stopped Working

The gauge on my 97, 300tdi stopped working after it overheated the other week. Following a replacement head gasket, I replaced the thermostat and the temperature sender which is in the head.

Funny thing is, I have no temperature sensor in the elbow of the thermostat nor is there any wiring for them. I have my suspicions that the car is a 'bitsa' - not too worried about that, more that I have a gauge that works.

Is there a fuse I'm missing or could it be the gauge or the type of sender.

Any wisdom gratefully received ...

There is a fuse but that shares other circuits such as the clock and other instruments, and yes it could be the other two suspects.
Remove the wire from the temp sender unit and ground it, switch on the ignition, if the gauge moves then the sender unit is faulty, if not then check the continuity of the wire back to the gauge.