Grounded Tach Wire Creates a Gremlin?

I8NEMO said

1968 Barracuda 340
All Elec. Components new including harnesses. Charging indication at Ammeter Normal since day 1

Key On Engine Off
Battery 11.95V
VR Blue 11.36V
VR Green 10.24V

600-700 RPM's Ammeter Gauge needle centered
Battery 12.V
Alternator 12.1V
VR Blue 11.7V
VR Green 10.58V

800+ RPM's Ammeter Gauge needle pegged on C
Battery 14.6V
Alternator 14.9V
VR Blue 14.2V
VR Green 7.6V
VR Flange to Negative Battery 21V, that's huge from what I've read.*

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Looking at your readings, I'd guess a defective alternator. First case, engine off, sense voltage (blue) is right at battery voltage and field (green) is nearly at battery voltage. This makes sense. Second case, engine below 800 rpm, field voltage at 10.58 volts and no indication of charging? With that much field excitation the alternator should be charging at a high rate. The third case, the regulator is decreasing the field voltage to less than the second case (7.6 volts) but now it's charging at a high rate as evidenced by the rise in battery, alternator, and sense voltages all being over 14 volts. Just my thoughts. Edit: Is it possible that you have a poor ground between the alternator and the battery? I know that's a long way from the steering column but....