Ford Repair: truck repair, serpentine belt, alternator

Question
Reinstalling alternator how do I tighten the tension on the serpentine belt for my 1999 f-150 4.2 liter v6

Answer
if you already have the belt on and it is not tight you have a bad tensioner or the wrong belt it has a self adjusting tensioner and when you use the wrench or square drive that fits it you either push or pull
to loosen it and the same to reinstall it-if you did that and tensioner did not spring back tight then it is bad. if it is springing back stiff
then the belt is wrong or routed wrong. good luck