I recently replaced alternator on 90 deville, and still had charging problems.Was told battery was bad, replaced it.Drove 60 miles to work and charge light kept coming on upon accelleration.car finally died.was told it was alternator, replaced again. now charging light blinks randomly but headlights go bright and dim during accelleration,but battery seems to be staying charged, any help greatly appreciated.
Well, you haven't many choices here. Battery has to maintain 13.2-14.2 volts running. You need to find the specs for amperage the alt should be putting out.
If the battery is good and holds up to a carbon pile test. Battery is good.
Now, you didn't say what you are using for alternators, but I am wondering if they are used. You didn't say, but if bought new at Autozone, they usually come with a lifetime guaranty.
You need a new alternator, not used.