Well, it isn't any more. The alternator was on my TR3A that got totaled a few years back :frown: The current TR3 still has what appears to be it's original Lucas generator from 1956 so I've been using that for now.
I don't have a diagram, but the description is pretty simple. I brought the output from the alternator out to a new tie point (really just a 1/4" bolt hanging from the wires), where all the new "high current" devices tied in (MSD ignition, electric radiator fan, high power stereo, headlight relay for 90/100 watt headlights). Also a heavy wire from the new tie point up to the original control box location, where it was joined with the original NW and NU wires (from terminals A and A1 of the original control box). I used 8 AWG wire as I had a bunch of it lying around, but 10 AWG would do fine.
The warning lamp output from the alternator/regulator joined to the original yellow wire in the harness (from the D terminal of the old control box). For my alternator (an old externally regulated Motorcraft), I needed to add a resistor across the dash lamp for it to work properly, but newer units may not need that. (The symptom without the resistor was that I would have to rev the engine up after every start, to get the alternator to begin working. The resistor also ensured that the alternator would continue to work, even if the dash lamp burned out.)
Otherwise, the only other change was the shunt across the ammeter. Originally, I used multiple strands of steel "handy wire" (aka "baling wire") and just added strands until I got about the reading I wanted. But during a later cleanup, I measured the resistance of the original ammeter (.012 ohms), and calculated that 3.5" of 16 AWG copper wire would make a 50% shunt (so half the current goes through the shunt and half through the ammeter, making it read 60 amps full scale instead of 30).
The original harness wires for the charging circuit were actually larger diameter than those on my Chevy with it's factory-optional 85 amp alternator, so I wasn't worried about the increased current through them.