Okay, the wiper switch was not working so I managed to get an original motorcraft switch, albeit 2 speed and my motor is a single speed. So wired it up and with the ignition on I tried the wipers. All okay, when I switched the wipers off they stoped in the correct park position. Great.
Went out in the truck today and used the wipers, but when I turned them off, the wipers just kept going. Stopping the truck and turning the ignition off stopped them but not parked. But as soon as I turned the ignition back on the wipers started up again, even though the wiper switch was off!! WTF! Any ideas what is going on? Not sure if the vehicle makes any odds to an answer here, but 1963 F100.