[dsraven]

something like a rotary fan switch may also work as shown in the link below. some highway trucks or chool busses etc use them. ensure you get one that will habdle the load.
check to ensure the motor operates before spending money on anything. you should be able to hotwire it with a fused jumper wire to the terminal directly on the motor, that way you aren't relying on some old wire thats been under there for a long time. if only a single wire connection then jump the wire directly to that and see what happens. if nothing then check the ground, possibly add a ground jumper wire to the motor body. try possibly moving the wiper arms to make the motor turn and therefore renew a contact with the motor brushes on the motor commutator, park switch or whatever. also look for a broken off terminal on the motor which could be a ground wire or possibly a mate to the other wire on the switch-meaning the motor would possibly have a power wire to the motor and the switch on the dash would run the motor remotely to turn it on or vary speed-like the set up ogre talks about except with a reostat on the dash instead of a cable operated style. if the wiring was ripped off at the switch end it could be due to a problem with the motor so the previous owner, or operator at the time of trouble, may have simply yanked the wires off to stop the smoke coming from the motor.
just a thought