The brightness of the headlights is a very poor indicator of charging system performance. That's what voltmeters and ammeters are for. An alternator that's doing its job right will produce a battery terminal voltage above 13 volts at idle, rising to 14.5 volts or more when it's running against a fully-charged battery at cruise speed. The condition and state of charge of the battery, not the alternator or generator, determines the operating voltage. Be sure the battery is fully charged and in good condition before blaming any other component for poor performance!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!