Hi: On the Hall sensor you should have 3 wires: 1 will be the 5 volt supply, 1 will be the 0 volt or Negative & the third will be the sensor squarewave output. It's easier to see the output if you've got an Analogue meter, connect the meter Black to 0v & the Red to the output wire. Set the machine to run & with a working Hall sensor you'll see the meter needle flick up to about 5v & off again as the sensor disc turns.