On the early cars just unplug your original alt. wire harness. You can leave your original voltage regulator hooked up to the engine compartment main harness and it wont ever know the difference. I do it this way so it still looks stock plus if I ever got into a jam and the parts house does not have G3 then I can just plug the stock G1 style alternator and harness back on the car and drive off. I started swapping these in about 1998 and I love the G3.
I also have built up the G1 's with both a 75 and 100 amp kits the problem with this is as you increase the overall output you loose the output at idle.
What I mean is that the upgraded G1 will have a little less output at idle then it had before the upgrade. The G3 the best output at idle between 80-90 amps!
I have a 70 bronco, 68 mustang and 90 mustang all running G3's, and one life time warrantee covers all three vehicles YEA!