Temp Gauge Won't work

You can also pop your gauge out and put a 25 ohm resistor in series with a 12 volt source and see if it moves. Tie the resistor to one lead of the meter and ground the other. Apply your 12v source to the end of the resistor. If it moves your meter is most likely good.

Basically the whole circuit in the car is really simple, it's 2 resistors in series with your regulated source. One fixed resistor being the gauge, the other variable resistor being the sending unit.