As with all of these over the internet diagnosis, I would question how is the original poster defining "Not Working!" Are we talking totally inoperative, no dash light, no movement at all. Or are we talking an incorrect reading, or a gauge going the wrong way when power is first applied.
Most gauges are electrical, which means that they are all essentially all volt meters that measure voltage to ground; with the sender being a variable resister. The gauge is calibrated to reflect the change in resistance as coolant temperature or oil pressure. The volt meter is as you would expect, but were not installed in older cars; but the ammeter is shunted and as such is actually also a volt meter.
Difference in ground potential from the supply side to the battery will affect the gauges accuracy. Polarity will have a real effect on the operation, and as mentioned the quality of the circuit (wire size, termination, and power tap) all affect how the gauges work.