ok. here is what i discovered. "if" the wiper is original, it will be a 6v positive ground and will not work on your rewired 12v system. but i did find out how the 6v system is wired for a 3 wire wiper motor. from the FSM :
there are 4 wires on switch.
1] turn control switch to "off" position by rotating it counter clockwise. remove the switch.
2] disconnect all 4 wires from switch. connect a test light between ammeter and terminal "a" on control switch. connect another grounded wire to terminal "f". the circuit should be complete in the "off", or parked, position.
3] turn the control switch to low speed [central] position. connect test light to terminal "b" and connect a grounded wire to terminal "a". this circuit should be complete. repeat with "b" and "f" terminals, which should also be complete. the parking switch is mounted on the motor and is a simple "make" or "break" switch, which opens the armature and feild circuits when the ramp rotates to the parking position.

the wires should be connected to the switch as follows :
green wire.... "b" terminal
red wire...... "f" terminal
black wire.... "a" terminal

the wires are color coded coming from the wiper motor.

this should be what you have on your motor now. but remember, this is 6v POSITIVE ground !
hope this sheds light on your situation.