I have a 1995 Rodeo. When it starts a belt squeals & voltmeter reads 8V Squeal stops @ 13v?

No, some other pulley is locking up causing the belt to slow down and lowering the voltage. You can remove the belt and spin each pulley listening for noise, feeling that the rotation is smooth, and that none of the shafts have any axial play at all. If there's an idler pulley or tensioner on the car, those fail as well. Could be the alternator or just a loose belt, but it wouldn't hurt to check. If you look carefully with a good light during the squeeling, you may even see a pulley stuttering or stopped.