While I can't give you any major help, it sounds like your problem would be
with the "park switch" that is internal to the wiper motor itself.
Basically this tells the motor when to stop (when the wiper is all the way
down in the "park" position.) If this switch is going bad, or perhaps if
the wiper motor is binding on something and not completely reaching the park
position, this could cause problems like you are experiencing...
While not a solution, hopefully it will give you a better idea of the most
likely cause of your problem.
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