1999 ford Windstar makes a squealing noise then shusoff what could be the problem?

Only when you stop the engine?

1) Incorrect alternator pulley.

2) Old serpentine belt is hardened.

3) Replacement radio uses too much power. Don't use it so much or install high-output alternator.

4) Serpentine belt contaminated with fluid. such as oil, power steering fluid, antifreeze.

5) Weak belt tensioner spring. Replace tensioner.

6) Replacement serpentine belt is too long.

7) Air conditioning system is overcharged. Noise will not occur with AC system turned off.