I havent looked at a wiring diagram but normally temp sensors are just a variable resistor that's temp sensitive and sits between the circuit end and ground. You just get one wire going to it. So if you ground the wire, you should get full deflection on the guage. If you dont I'd say the guage is stuffed. But unless they are shorted guages are pretty damn reliable so I'd be looking for a wiring fault somewhere before ripping it out.