Why is lighting system "dimming"or "glowing"? This is a follow up inquiry.

What is your question?

One mechanic said it was a grounding issue in lighting system. First replaced alternator lasted 4 weeks, then voltage hit 18v. Second replacement o.k. for a week now. What is the probability of a "grounding" issue. If this is true, will it kill another alternator sooner or later? Lighting and charging are normal at present.