Haha status quo, Bob is all mixed up! OK I am pretty sure on this one. You have a "3 Wire" GM 10SI alternator. The wire that is not hooked up would have gone to the indicator light on the dash. The wire that is hooked to the ignition switch is exciting the field of the alternator. What someone has done is made a GM 10SI into an effective "1" wire alternator. When the field of the alternator has less voltage than the output of the alternator the alternator will attempt to charge (LarrBeard did I get that right?) So by hooking it (the field wire) to the ignition switch, when the key is on, 12 volts is applied to field causing the alternator to charge. I would say it is hooked up in a fashion that should work fine. Now if the internal voltage regulator in the alternator is leaking it will slowly drain the battery. Refer to the other thread! Oh my.
I am going to go out on a limb here and state this on paper:
I believe the absolute best solution to an easy 12volt clean trouble free bolt in solution to a 6 volt system is a one wire. This is so easy to do it should be illegal. If you have to buy a new alternator don't waste your time on anything but an internally triggered "One Wire". Just remember they start charging at a set RPM. So the first time you rev the engine it starts to charge. This is the one thing that causes the most confusion on a one wire.
I found it interesting that the writer makes this comment:
"High output aside, don't expect your alternator to do anything for you at idle speeds. Alternator output increases with rpm, even a 100amp unit won't put out much more than a 63amp unit at 1000rpm. If your using underdrive pulleys, this may highlight or worsen idle output problems."
Both old coots agree that it should work - something has gone wrong.