It sounds like the park switch on the wiper motor has failed in the closed position. When the wiper motor is shut off at the switch, a cam in the wiper motor engages this switch until the wipers come to their resting position; whereupon the switch should no longer be engaged by the cam and should shut off. Try disconnecting the lead to the park switch (this is mounted on the wiper motor, but the wiper motor does not need to be removed to access the connector). If this corrects the problem you can run the wipers temporarily without the shutdown feature and replace the switch as soon as you are able to replace it.