Sean,
Does your Pantera possibly still utilize the oem voltage regulator? Electro/mechanical voltage regulators sticking open or closed was a common electrical system failure, back in the days of electro/mechanical voltage regulators. They have solid state replacements that drop right in without any changes to the cars wiring required. I am in agreement with Larry & Derek that your problems sounds like classic voltage reg trouble.
Of course, there are modern high output alternators available with built in voltage regulators, they will require a bit of simple rewiring.
your friend on the DTBB
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