I ended up doing the same, buying one from NPD. I measured the resistance, or should say attempted to, while on the bench. In one direction I saw 1 kohm, and in the other it was open. The thermistor is not a simple resistor, so that should not be shocking. Sorry for the electrical pun, I couldn't resist.
Then I installed it in the trunk. I had the thermistor loose, not attached to the sending unit, so I used two jumper wires to complete the circuit.
At 13.2V (Ign), with the thermistor in the air (shop temp ~70F) it took just under 3 minutes for the thermistor to heat up enough to turn the low fuel light on.
When I submerged the thermistor in a small cup of water, the light went out almost immediately. After extracting the thermistor, it took another 3 minutes or so for the light to come on.
I'm including this information so that (1) if you don't measure resistance on your thermistor, you don't necessarily have one that is broken, and (2) you know the timing involved so that if you do your own test, you don't give up too soon and start spending more money!
John
