1998 mercury villager van , power steering belt was sqealing, so I replaced all three and it still sqeals and its still the power steering belt thats sqealing. I tried tightening it and that made the belt sqeal and loosening it some made it sqeal very loud when turning the steering wheel I could'nt find any in between any ideas?

Four years later, this answer will be for anyone else interested. And just a guess. First, the mere act of dripping some anti-freeze on a belt or pulley can lead to squealing that will stay that way for a long time.

Lacking the above remedy, after removing the belt, try spinning the power steering pump pulley to make sure it rotates easily. Bearings could be shot. That could make the belt slip while struggling to spin the pump. Also any bearings in the idler pulley.

If not there, check alignment of the pulley with the other things (other pulleys) it wraps around. Alignment is checked with a two-piece laser tool (e.g: Dayco). Or I saw recommended merely tying a string around two areas to see where they cross in the middle. Look up that idea for better instructions.

CHECK ALL THE PULLEYS WITH BELT OFF TO SEE IF ANY HAVE PLAY IN BEARINGS
OR ARE CONTAMINATED FROM PREVIOUS BELTS SLIPPING MAKE SURE THEY ALL ROTATE FREELY WITH NO SOUND