You should beg, borrow or steal someone's AutoSound 2000 Technical Brief for October - November 1992.
In this publication, Dave Navone and Richard Clark demonstrate a very simple way to see if you need a High Output Alternator, additional battery, or Capacitor.
This subject was again brought up in the December 1994 issue, since people are always talking about dimming lights, upgrading alternators, etc.
Anthony Granatelli