And check the alternator connector - follow the cable coming out of the alt to a 2-pin connector. Separate the connector, clean and grease the terminals in both sides of the connector.
follow the Beaver's advice on this one before going further....
follow the 2 wire line up to the connecter, and examine it closely....this is a very predominant problem spot in the charging system, and many many people have a melted connector there.
insure it is intact, and both sets of blades are clean and in good shape.