Finally got the generator light to go off! What fixed it was seperating the D+ wire from 61(which powers the gen light). The new regulator I installed at the beginning of this little adventure wasn't exactly identical to the old one - the 61 and D+ terminals were seperate on the new one but were combined on the old one.
Oddly enough, the diagram on the regulator and in the Haynes manual suggest that 61 and D+ should both connect to the same terminal, so we wired it that way the first time. We got continuity between the D+ and 61 terminals on the regulator, so thought it would work anyway. Guess not - once they were seperated, she started right up and the light went out almost immediately.
Thanks to everyone who posted all the great suggestions... much appreciated!
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1966 1800S in sunny Sandy Eggo

AAAARRRRGGGGHHHHH!!!!!
It's back on after driving around the block, fighting up a steep hill that almost stalled her (why she has no guts is next on the list - the carbs are my first guess, but that's Advanced Volvo Antics).
I'm totally at a loss... I checked all the connections on the regulator that were the cause last time.
Why would it work for a time and then quit? Any thoughts??
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1966 1800S in sunny Sandy Eggo

Were both of these Bosch regulators?
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George Downs, Bartlesville, Oklahoma, Central US

Yup, both are Bosch. The have identical cases (of course the new one is shiny). The only differences are the seperate terminals and origin - old one: german, new one: brazilian.
The other item I should have mentioned is that the local automotive electrical shop I took the generator to for testing initially said "it needs to be rebuilt" but when I pressed them for details, they admitted that it was putting out proper amounts of power but they "suggested" the armature and bearings be replaced cause they were "noisy". Yes, I know, that should be done, but it would not have fixed the charging problem... and it would have been around $100!
Caveat emptor!
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1966 1800S in sunny Sandy Eggo