clean the contacts of the blue and white wires going into the alternator.Also clean the contact of the red wire going to the alt.If that doesn't do it,check the voltage at the red alt. wire.Should be around 13.2 volts.Check all the contacts (4) going into the voltage regulator.If the alt. is putting out the volts,and all contacts are good,could have a faulting voltage regulator.The old style voltage reg. had movable contacts (relays) that can wear out over time.If you have narrowed down to the regulator,buy a Wells solid state unit fron autozone.