1969 Formula S owners needs help with Variable Speed Windsheild wipers

Ok.
What concerns me is you say your motor won't shut off.
Under that cover is a copper plate shaped rotary switch.
When you move the switch too "off", it changes the power feed THROUGH that switch.
When the contacts hit a gap in the plate, no power.
I have one on a B body like 4spddragtop's that I took apart, cleaned and adjusted.
I can post pictures and a simplified wiring diagram if it gets to that.
(Chrysler treated the wiring as an after thought on the wiper motor.)
Unfortunately, my B body came with a two speed switch.
Yes, that will work with a variable motor.
There is a thread on here about motors and adjusting that switch.
I believe your motor has some markings on it to do that.
But they are different from 4spd's.
You rotate the plate to make it stop in the right place.