Alternator Light ON most of the time, How do I determine what's wrong? Options

[ThinAir]

I HATE electrical problems!!!! Okay, with that out of the way... here's the deal.

My car went 800 miles round trip for Red Rock Classic with no problems at all. When I shut the engine off in the driveway I had no glowing alternator light. A couple of hours later I start it up to move the car and the alternator light is on. I ran the car some to try and determine if it was really on or just glowing and discovered that the light went out and seemed to be tied to the engine rpms.

Well I've tried to tighten the belt, but have gotten no different results. Most of the time when I drive the voltmeter is sitting just under 12 volts and the light is glowing dimly, but if I am idling the light is on strong. Once in awhile the light will go out and the voltmeter will show 14 volts, but there is no consistency to it.

The AA Tech Tips book says this:
Condition:
Light off with key off
Light on with key on
Light glows dimly when car is running
Problem:
Bad diode in alternator or bad ground

Since tightening the belt has not made a difference, it seems like it must be one of these things. The question is how do I tell what it is?

Since the car starts consistently I know that the tranny ground strap is well connected and that's been confirmed. Since the alternator grounds to the engine case, where else could there be a bad ground?

[ThinAir]

Clean contacts for the alternator wiring harness didn't do anything either. I'm running a new Bowlsby harness so I'm sure it's good.

I looked in the Haynes & VW manuals and both describe a procedure for testing the alternator that involves a Sun battery switch and looks really complicated. Isn't it possible to put a multimeter from the brown lead to the red or green and measure the direct output of the alternator? If it is, which do I pick? I'm assuming I'd be looking for 14V. I just don't want to ruin an alternator by hooking up something wrong.

Looking at the Haynes wiring diagram, I can't really tell where the stuff from the alternator goes. I see where it all goes INTO the VR, but I don't see how anything comes OUT to get back to the battery! Someone posted diagrams of the major circuits a long time ago, but I haven't managed to find them back yet.