Very commenon with these electrical systems. Do you know what the amperage rating is for your alternator? I used a 65 amp alternator with the correct round back on my 68' Coronet. Big difference, virtually no dimming of the lights. The alternator I used was one from a 72' Chrysler Neuport. That year Neuport used the round back alternator which is correct for your 69' Coronet. You'll love the improvement.