The one-wire set-up will ground the alternator thru the brackets....shouldn't need a separate ground wire. Just un-plug the connector that goes to the old alt, and connect the one red wire. You should be able to leave the old external reg plugged in, and on the car, with no adverse effects. If you do go this route, please ask them if the one-wire alt they provide will drain the battery over time.....I've head MANY stories about folks using one-wire alternators that would drain the battery in a couple of days(or overnight), and also heard that some alternators will "buzz" with the key off, due to them still being active. Never actually had these problems myself, but...