01 Windstar Rear wiper

The rear wiper began working erratically and has actually come loose but had fortunately not fallen off. I think I have screwed it back on properly but it does not wipe back and forth correctly, so consequently I don't use it. How do I set it to wipe correctly?

Thanks.
Miles

Make sure you dont over tighten the nut not sure on how much torqe is to be set at but your wiper in off . should be resting flat to the passanger side.at the bottom of the window. hope this helps..