Car has been sitting since it's developed a strange parasitic draw from the battery. New battery in one day, the next morning, flat.
May be the replacement alternator giving you grief.
May also be something drawing current that should not be. The glove box light was a persistent culprit in my 242GT, as the glove box door warped slightly.
As Snoopy suggested, it's multimenter time. See if there's a current flow with everything switched off. If there is a flow that shouldn't be there, pull fuses, one at a time, until you isolate which circuit is causing the drain.