whenever i drive my 68 malibu at night, it seems as if at idle my dash/headlights are dim(not dim to the point where it is a problem) but when i accelerate, my dash lights and headlights get brighter. I have an internally regulated alternator. I have read that voltage regulators may be the cause of this. Is it possible to change the voltage regulator in an externally regulated alternator? How hard is it to do, or am i better off getting a new alternator?