<VV> Another glowing Gen Light question - No Corvair

[grant young]

This problem is on my '72 Caddy hearse, but since the charging systems are similar, I thought I would try youse guys. The problem is a constantly on generator (alternator) warning light. I have checked all the wiring and replaced part of a suspicious one from the alternator to the gauge. I had the alternator checked (100A with less than 500 miles on it) at AZ and it tested fine. I replaced the pigtail plug , just in case. Also swapped batteries just to rule that out, and no change. What to check next?
Thanks,
Grant