Alternator/brake light flashing on and off

Okay, this winter had the symptom for a few months of the alternator/brake light coming on and off ( head lights would dim then back to normal ) and until it went into limp mode and shut off on the freeway in a snow storm. Had it towed home and charged the battery that was six months old and it started and ran good. The car sat two months until I got around to replacing the alternator. This is my son's car and he just told me today that the same dash lights are flashing again only faster flicker. At idle no dash lights come on but when you rev it up they come on and flicker then let up and they go off. The head lights do dim when the dash lights come on. I felt the circuit breakers under the hood and didn't hear or feel anything. Going down the road with the higher rpm they are flickering most of the time. Any suggestions?