Explain the 3 black wires and 1 white wire coming out of the Model APG gable-mount power vent thermostat.

Here is information about the wiring for the APG Gable-Mount Fan.

There are a total of 3 black wires on the APG powered attic ventilator product. The first black wire is coming from the motor into the thermostat box. The second wire is soldered to one side of the thermostat control. These first two black wires are connected together via a wire nut. The third black wire is soldered to the opposite side of the thermostat and has the insulation stripped from the end when it leaves the factory. This third wire should be connected to the hot wire coming from the service panel. The white wire from the motor connects directly to the neutral or common wire from the service panel. Finally, a ground wire should be attached to the green screw with the cup washer on the bottom surface inside the thermostat.