I wish I still had my Century service manual (I had a '92).
I found three parts for the wiper system. The motor ($100), the pulse board ($50), and the stalk/switch ($300). Then there's the various linkages, cogs, and gears connecting everything together.
A bad pulse board would not supply enough electricity to the motor for the wipers to drop down into the off position when they're switched off. That would be the easy fix.
Just my two cents.