I was wondering why there are two forward gears. You are told to use forward one. There is forward two, which isn't mentioned. When would you use forward 2?
If I'm not mistaken, i think forward 1 is running the electrical motors in series and forward 2 is running them in parallel. Basically, electricity is either supplied to the motors via a single channel that supplies all motors, or supplying each motor with it's own channel, thus increasing the combined power output of the motors. Maybe.
IIRC, that is how the speed controller works on these trains. On the '72 the positions are even labeled series-parallel-shunt. I'm pretty sure the switch in question simply limits power by dumping off through a resistive load.