You're right. Likelihood is interesting speculation, and on further speculatin' I wonder if the loose green wire was one of the fancy things in that era, only available in the "lux" cars, called central locking. A common reason for battery drain when it messes up.

Someone may have found the wire for it and disconnected, while troubleshooting a drain. Green is the color for wires feeding loads that would drain the battery overnight.

If not central locking, there are the usual suspects: delayed courtesy lamp, glovebox, under hood, trunk, antenna parking, remote trunk release, clock, radio presets. Something it came with probably doesn't work with that wire loose.

The numbers on the sleeve might help; I have a parts manual from that era.
--
Art Benstein near Baltimore

A skeptical anthropologist was cataloging South American folk remedies with the assistance of a tribal Brujo who indicated that the leaves of a particular fern were a sure cure for any case of constipation. When the anthropologist expressed his doubts, the Brujo looked him in the eye and said, "Let me tell you, with fronds like these, you don't need enemas."