I'm trying to wire my wiper motor but can't figure out which wire does what. It's a 47 desoto and there are 3 wire coming off of it. I rewired the whole car with a universal 12v harness from speedway motors.

if it's the original motor, it will be a 6v and won't be compatible with your 12v system with out some kind of voltage reducer. just to hazard a guess would be a hot for low, one for high, and a hot for the park circuit. i'm guessing the ground for the motor to work is at the motor mounting point. i'm just throwing out things here. how many wires connect to the switch ?

6v POSITIVE ground vs 12V NEGATIVE ground

http://www.examiner.com/article/the-6-volt-to-12-volt-dilemma-mopar

Towards the bottom they talk about wiper motors.

yes, the positive ground. i forgot about that ! gettin old sucks ! i dug out one of my desoto FMS's. i'll crack that book to see if i can gain any insight. upon further reflection, most cars of this era were single speed wipers, and could have been vacuum units as well. i had a 48 plymouth once, that had electric wipers, but it could have been a retrofit unit. i don't know. when i rewired it, i installed a modified vw bug set up. that worked very well. i'll report back after a spell with what i find out from the desoto FSM.

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.

Yes I'm aware of the 6v-12v issues. Its the only part left on the car that is 6v. It is original to the car. Thanks for the info.