ZW 944

I just replaced my turbo's electric water pump, when I found out that the old one never really ran like it was supposed to. Then I looked into it after I installed the new one, because the new one doesn't run when the car is shut off. After some reading I grounded the temp sensor wire to the chassis, and the pump ran for the 25 seconds its supposed to, but during normal operation of the car, the pump never comes on. I'm suspecting the sensor is the culprit, but I wanted to get some input on here before I went ahead and bought one.

How exactly does the sensor work anyways? it only has 1 wire connected to it. or is that metal pipe its screwed into a ground also?