I'm not real sure exactly how the system works. However, the wipers on my 68 didn't work when I bought it. The switch,harness and wiring were butchered. I replaced the harnesses and switch. Found that the power to motor goes directly from the fuse to the motor windings. The switch merely "grounds" the windings to complete the circuit. Thats why it is so important for the switch to have a good ground at the dash. This is where the circuit is completed. That's about all I know. Someone more knowledable may shed more light on this. The three tabs on the switch are for the low, high, and washer pump circuits. I don't remember which is which, but there is a light blue, dark blue, and black wires that go from the switch to the motor conn. the yellow wire at the motor is the 12 volt source.
[This message has been edited by H-dog (edited 01-03-2001).]