That will be.......
Black ........ reference signal out
Grey ........ Nuetral
White ...... Heater
If you want to test the sensor,take it off car & clamp in a vice,connect a multimeter (set to 0 - 5 volts range)across black + & Grey -,heat the element with a blowlamp as the element caseing comes to red heat it should have a reading approx 1volt,now play the flame off & on the voltage reading should fluctuate accordingly.
If that wiring section works the fault must be deeper in the loom
