My temperature gauge is inoperative and I'd like to debug it by starting with the sensor. What is the sensor supposed to do? Is it a thermistor or a thermocouple? If its a thermistor, what is its resistance supposed to be at room temperature and operating temperature? If its a thermocouple, what is its output voltage supposed to be?

Assuming you're talking about the stock sensor in the taco plate on later engines, it's an NTC thermistor, with resistance going DOWN as the temperature goes UP. If the sensor has failed, it will usually show a fixed resistance or be open (infinite resistance), so you can check it easily enough w/o knowing the correct resistance values (which I'd tell you if I knew them).