Maybe the wiring at the motor itself is to blame then? It should be easy to check to see if 12V is present at the motor connector from the pod switch and eliminate that if it is shutting off.

Since the wiper's parking system has 12V applied to it even when the pod switch is in the off position I guess it is possible that a short in the parking switch mechanism could apply power to the motor at all times...again I am just giving my best guess but have you opened up the motor itself and inspected the park switch? Usually when I have seen these fail on other cars they fail so the motor just stops where you shut it off, but I suppose it is very possible that the park switch mechanism could keep the motor running too if the park switch was stuck closed.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz