Your problem sounds like a "fusable link" is blown. A fusable link is a wire that acts like a fuse and melts should the power spike. This protects the battery from damage.Most charging systems use this rather than an inline fuse to protect the battery.
If possible, follow the heavy gauge output wire back from the alternator to the positive post of the battery. That wire should have battery voltage at all times. If a voltmeter is handy, check it. Usually the link will be spliced into that wire very close to the battery so look around for a melted wire.