Erratic Temp Readout-SOLVED

I was experiancing unusuall readings on my dash for the engine temp.-either too low or too high in my 93 4.3L CPI "w". I knew it was incorrect because it would read hi temp. on a stone cold morning. The sensor is actually head mounted (pass side) not on the intake manifold. Anyway I decided to replace the sensor because the dash readout seem to respond correctly when I unpluged the sensor. A trip to Autozone for a Wells TU152 ($15) solved the problem allthough Autozone calls it a temperature "switch". Does anyone have any ideas why a variable resistance device is called a switch????????????