My rear windshield wiper arm broke. The motor still works, but it doesn't stop at the edge of the window, it will go the entire 180 degrees. The wiper will stick out the side of the car and look really silly.

Do I need to replace the whole arm? Or is there some part that tells it it to stop at the vertical position?

 

If that happened to me, the cheapest route I would go would just do a wiper delete and plug the hole. IMO rear wiper on the Z looks sketchy. But since mines functioning I just kept it on there, even though I never have to use it.