Sounds like a pain in the shorts, but with a set of wiring diagrams and a meter any good electrical guy should be able to sort it out. You just may need to become a good electrical guy.
Your 230 miles from Roger in Double Oaks (outside Dallas), but I think there are a few guys in Austin area that might be able to help out, read the diagram while you crawl under the dash, that sort of thing.
Alternators have two wires, big fat wire going off to charge the battery, little bitty wire that wakes up the alternator and gets it excited enough to start making current (generators have magnets inside, alternator don't). On the 928 the exciter wire comes from the battery through the charge warning lamp in the dash and goes to the alternator. Later on Porsche put a resistor in parallel with the lamp since in the old design when the lamp burns out and alternator doesn't charge.