wipers dont work on 1999 grand prix

And then when you turn them off it parks half way up the windshield, right? My '03 does the same thing from time to time. The wiper arm is slipping at the point where it bolts to the regulator shaft which is the shaft that turns back and forth and moves the wiper across the windshield. Get the correct sized wrench for the nut that holds the wiper arm to the car. Open the hood so you can get at it properly. With the wipers in the off position, loosen the nut a bit and manually push the wiper arm back into its proper position, then re-tighten the nut. It needs to be very tight, although I suppose it would be possible to break it off if you over tightened which is something you definitely do not want to do, so use common sense. Restart the wipers. The tip of the blade should travel to the very edge of the glass but not travel beyond. If it still does repeat the process and push the wiper down a bit further. This is likely only a temporary fix, so keep that wrench in your car at all times so you don't get into trouble on some dark and stormy night in the middle of nowhere. I have to retighten mine once or twice a year if my wipers get frozen to the glass or have to push heavy wet snow. Its gradually getting worse so at some point I may have to bite the bullet and replace the regulator, but that is not a project I'm looking forward to. I may eventually just epoxy it on and take my chances about ever having to get it apart again. Hope this helps.

Tightening will work for a while. I replaced the wiper arm on mine. Part was only like $30 at dealer. Junk yard wanted nearly as much for used one.