Water temperature sensor? if canadian car it has an extra switch for water temp.
both us and Can cars have the sensors for water temperature just under the thermostat housing ( front of engine, right beside the valve cover ). you will have 3 or 4 sensor there, thermotime, water temp and one other, can't remember name right now
I do not have the book with me but I would assume that is where your getting your signal for the guage in the car. However, if your water temp sensor connection was bad then your car would run bad or not run at all, so I would lean towards the connection in the dash to the display?
I may be wrong though, never had that problem, nor knew anyone that did.
later
Ryan