Bare bones 3G wiring:
On your alt's regulator, you should see A, S, I.
A = battery voltage. Techically you can loop this to your load-bearing connection on the back of the alt.
I = find a wire that is key and cranking hot. Tap into this and splice a 500 OHM resistor into the wire. Then have the wire continue to the I terminal. Do NOT connect a straight run of wire from the ignition source to the I terminal. The OEM circuit has the resistor and an idiot light wired in parallel should you desire to have a light too.
S is the stator wire. Loop this to the long spade receptacle on the 3G housing.
FWIW, you can buy nice little regulator connectors that are made for this kind of retrofit. The one from FFI should be a very nice piece. I haven't used it but do have one from PA-P. They function the same as a conventional connector but have terminals for a clean install.
Good luck.