Mark, a thermistor is not a simple contact closure. Thermistors are resistors that change their resistance with temperature, either increasing or decreasing in resistance with a change in temp. (They come in two flavors called positive or negative coefficent.) The idle thermistor in the Delorean is used to alter the idle speed setpoint depending on coolant temp. On my car a custom circuit is used to exploit this function so as to increase the idle 200 rpm when I have the headlights or A/C on. This sensor is not on or off like a switch. You can't look for a contact closure, you need to measure it with an ohmmeter while you change it's temperature. The spec escapes me at the moment but if it changes resistance (somewhere below the 10K ohm range as I recall) as you heat and cool it, then the odds are it's probably working. Use only an ohmmeter, if you pull to much current through it (by using a large 12 volt test light for example) you could damage it.