95 mercury windshield wipers will not park what is wrong?
There is what is known as a park pawl in the transmission of the wipers that activates a switch when it goes to park. There is a set of contacts in the wiper transmission that has to make contact to cut the juice to the motor when the wiper switch is off and the wipers are returning to the park position. It could be bad as well as the other suggestions already mentioned. Not very familiar with your particular motor, but if has delay wipers and such the GM motors have a printed circuit board that goes bad and can prevent them from parking as well. Ford might have a board like that but can't remember. Boards for the GM's are cheap and can change without removing the motor. Imagine Ford would be similar. Can also cause the wipers to come on for no reason or the intermittent to vary wild in time regardless of where you have the delay set.
The windshield wiper transmission may have slipped a couple of teeth. Do the wipers seem to wipe past the edge of your window? If so you can take the transmission cover off and loosen the bolt or clip, and reposition it to where it should be when in the park position. Then reinstall clip or bolt and try them out.
