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You will not see an AC voltage signal on this type of sensor. It is a Hall Effect sensor and it triggers DC On/OFF. That is the advantage of this 3 wire sensor over the Induction , 2 wire sensors [ they are AC V output]

Your sensor has a 12 V feed from the ECU [+ and - to power the IC of the sensor] and the third wire is the triggered on/off signal back to the ECU.
So, you want to see a constant 12v at the + and - pins, and a pulsed, DC signal at the third pin, which is the sensors switched output signal to the ECU. This is a switching sensor, unlike the 2 wire AC voltage generator sensor .......

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A Dalton