Here is a picture of the shift box and photo 2 is a wiring diagram.

https://plus.google.com/u/0/1126369...6836972546&oid=112636930370126476644

In this illustration the limiting switch is called the automatic switch. The part they call the drive screw is what shifts the axle. The electric motor is reversible and when the block reaches a certain point it breaks connection in both directions. The shifters were bad about collecting moisture which damaged the thread on the drive screw and the often the bearing at the bottom got rusty. Eaton used this same electric shift assembly until about 1985. I have my best luck finding NOS electric Eaton parts that were originally sold by Ford. There were a lot of Fords around and they didn't fool around with the vacuum shift that GM used for so many years. International is also a good source because they also used electric and a lot of little towns had an IH dealer.