temp gague

I have a 1996 fiat cinquecento 900cc sx which came with just a speedo and a fuel gague as standard and nothing else I have fitted a set of sporting clocks and wired the rev counter in and everything else works execpt the temp gague I have been trying for some time to figure out how to wire the three contacts in to get a correct reading but have not had much luck and on occasion it has caused the warning light for the injector to come on when contact was made with the coolant temp sensor on the thermostat housing for some reason not sure why. Can anyone help with a wiring diagram or simple way to wire it up ???? I dont want to fit an aftermarket one which would mean drilling into the head or thermostat for the new sensor peg !!!!!!!