96 Ranger Electrical Problem

1996 Ranger, 2.3 engine, 131K miles, battery light came on yesterday, tested the battery both under load and free, found low output from the alternator, and battery wasn't holding a charge. Replaced alternator and battery this morning, and the battery light stayed on. Does this need to be reset somehow? Starts fine, all electrical accesories seem to be running fine. Any ideas? James F. Hodgdon Jr. Hodgdon Scale Models