Alternator Upgrade Checklist.

I did as 67Dart273, using a 95 Jeep relay box (search for my post). If your lights dim while idling, that is sympomatic of voltage drops thru the bulkhead and harnesses. They should be bright from just the battery alone. The alternator's purpose is to recharge the battery.

Insure that the new alternator doesn't have a built-in Vreg, since many do. If just a simple 2-wire field, you could get an electronic Vreg for your 66 Dart ($11 rockauto) that hooks directly to your existing wiring. At the alternator, just wire one terminal to ground (case of alternator). Not sure, but I think you will need a different adjustment arm for the new alternator. It needs more curve to hook up to the adjustment bolt.