Water temperature gauge

Hi Guys,
Anyone got any suggestions? I've just put together a 1991 K100RS4v (VIN 0201103), it all runs but as soon as I turn on the ignition, the water temperature gauge goes right over to the end stop at the 'hot' end of the scale - and that's before the engine has been run! I got to the temperature sender unit behind the radiator and disconnected it but the gauge still went hard over. Is there only the one temperature sender on my bike or is there a second one? If so, where is it? I've seen a US web site which suggests that there is a second sender just for the gauge but I can't find it if there is :question:

Hi

Silly thing, but maybe wires are swapped at oil switch and temperature sensor on water/fuel pump

These sensors are quite near and connectors are similar. How does oil pressure light work? Does temperature needle fall immediately after engine start?

Regargs,
Viktor

Blowed if I can see the second sensor - I can find the one behind the radiator but there appears to be a blanking plug in the water pump - I must be looking in the wrong place! However, the 'lack of earth' idea prompted some serious cleaning of contacts and, viola, i now have a working gauge. Looks as though earths could be fun on this old girl!
Thanks guys, that's another problem solved - back to brake bleeding - "bleedin' brakes!"