Glad you got it fixed.
Did you see any whitish stuff on the battery posts or connectors? It sounds like the battery post/connector that you removed may have had some corrosion that was causing a high resistance connection. Removing/replacing the connector cleaned off enough corrosion to make a good connection.
If you think corrosion may have been the problem, remove both connectors, clean terminals and connectors with a wire brush until all corrosion is removed, then put a VERY LIGHT coat of bulb grease on the mating surfaces before reassembling. Check for corrosion during your periodic inspections.
If your windows or other electrical items are acting up, search this site for "window reset", &c.