Kevin,

first things you might want to look are the ground strap(s) (battery,
tranny,waterpump).  They could be corroded, cut etc.  If your engine is not
properly grounded the charging don't work proberly.  Also if the alternator
is loose in its bracket could make this huge voltage drop.

Juha Koivisto
88 Vanagon (Caravelle) 1,6TD (old school bus with 9 seats)
TURKU, FINLAND