68 and 72 wiring should be about the same. I have nothing but some generic diagrams and don't even have a scanner to get them into this computer or to this site.
Know that with the external regulator some things are funky. You may need to get a new one. Still available new as far as I know.
The alternators use a diode trio and will charge when one is blown but only about 10-20% of possible power and used to give a dim "GEN" light that might go out with some RPMs. That trio can fail with just messing with the wiring -- I know that.
I can't help much more with specific ways to change this for you. If you can get your hands on about any 68-72 diagrams that would help. There on the web somewhere but I wouldn't know where to start looking. Too bad I threw out a complete set of books for an Olds 88 for 1968 that listed every screw in the car and diagram.
All this stuff exists I just don't know where right now. You could wing it with just generic ways to hook these things up as I don't think they were unique to just GM but who knows now.
It's of interest so let us know if you have any discoveries with this.
Funny: I still deal with a 1948 generator set up as 6V pos ground. Talk about a mind game to figure that sucker out. It's OE amp gauge still works and is manually regulated by a lever/switch for high and low rate of charge. Those were a nightmare back when and still are when anything goes wrong.
Good luck - keep us posted,
T
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Tom Greenleaf - MetroWest, Boston