After installing a new alternator, the serpentine belt will not tighten?

BELT ADJUSTMENT
Tensioners are used to automatically adjust belt tension to specification. Belt tension should be about 178-311 INCH Lbs. (78-137 kg). Check belt for fraying. If fraying exists, ensure belt and tensioner are properly aligned. See Fig. 1 . Tensioners will contain a belt-wear indicator. SeeFig. 1 -Fig. 7 . If tensioner reaches travel limit, as indicated by marks on tensioner, replace belt. Ensure serpentine belts are properly installed. See Fig. 8 -Fig. 20 .
Fig. 1: Checking Serpentine Belt Alignment

I can't show you a belt routing diagram without knowing the exact engine size of your vehicle ?