The wires labeled B are power, pin closest the smoke bowl is AC hot, pin in the middle is AC Ground. The 3rd pin (furthest from the some bowl) is chuff input, which is not used on diesels.
Not sure what A is connected to, assuming +5VDC from the regulator and ground? If so, these go to the fan motor.
The question marks were the fan motor, but requires the chuff input to work properly.
hope that helps!
Mike