Originally Posted by Rod Stewart:
I am very curious about what that switch is used for also.
Rod
It is used to switch the dual motors to apply voltage in series(positive voltage starts at one motor and negative ends at the other and parrallel(positive and negative voltage is supplied to the motors individually. In series the engine runs slower(more prototypical)slower take off. Parrallel it is faster(more powerful). Dual motor locos are wired normally in parallel.