Wiper motors have battery power supplied directly to the motor as well as ignition power.
When the wiper switch is turned off, the battery power continues to supply the motor with power until the wipers arrive at their resting place. Inside the gearbox is a limit switch oriented to shut the wipers down when they reach the PARK position.
A broken limit switch inside the wiper gearbox would cause this. So would a fried wiper pigtail battery power terminal. There is no way to defeat the auto park feature except to turn the key off while the wipers are in action. So, the clue is to check battery voltage at the connector to the wipers. It's time to grab a 12-volt test light and access a factory wiring diagram. Blind parts replacement try-it-and-see is a poor diagnostic substitute.
