lights/voltage problem

73 Dart, w/360, MSD coil and box. Have a new (remanned) alternator (55 amp) and new voltage regulator both from NAPA. With engine warm and idling, turn the lights on, and they dim badly, give it some gas and they brighten up. The amp meter in the cluster is down to about negative 10. Anyone have an idea to the problem and a fix?

Thanks,
Eric