"After getting involved with repairing an MTH 785 reproduction of the original American Flyer Coal Loader, I could not find a schematic of the wiring. MTH chose not to use the magnetic reversal of using two field windings in an AC motor, and instead chose to use a DC motor. They accomplish motor reversal by using diodes in the control button to reverse the polarity of the voltage to the motor..........." 

Here is the wiring schematic Jim created.