JUST MY HUMBLE OPIONION...
there is so much wrong with this wiring that I would get a doner car or aftermarket OEM replacement wiring harness for your car.
If your car started life as a /6 and it is now a V8 buy a year correct V8 engine harness.
Lastly please do as I mentioned earlier about measuring the resistance of the two field wires and report back. It is posable that your alternator has one of its field wires internally grounded, so a single wire to the other field would cause the alt to charge.
How it would be regulated.... Maybe the blue wire is going through a resister of sorts, to get the voltage down to 7 to 10 volts effectively regulating the alt to not over charge. Or it has beenhooked to 12v and overcharging all along.
