If you haven't swapped a regulator/brush assembly before, I recommend you pull the alternator and do this on a workbench the first time. Once done, the practice would go a long way toward being able to do this with the alternator in situ next time.

--
Art Benstein near Baltimore

A woman has twins and gives them up for adoption. One of them goes to a family in Egypt and is named "Ahmal." The other goes to a family in Spain; they name him "Juan." Years later, Juan sends a picture of himself to his birth mother. Upon receiving the picture, she tells her husband that she wishes she also had a picture of Ahmal. Her husband responds, "They're twins! If you've seen Juan, you've seen Ahmal."

classic bad voltage regulator symptom

Also check the ground screw under the plastic shroud around steering column. Mine was loose and causing similar problems.

Most likely just worn brushes...they are removable if you desire with alternator still in place.