[hpaulb]

On the sending unit, one wire is ground reference and the other is a resistive output. One has a nut and the other has a slip on spade lug. Both are covered with a rubber hood. Pressure wash the area to get rid of all the grime. The wires feed up through the front under the belt cover between the water pump and go under the intake manifold to the rear then into the large bundle.
Stick an ohm meter on the resistive lead and measure. That should narrow down the sensor ground, sensor itself or after in the wiring/ Gage.