This is one for the books, so I thought I'd better share it so that if I've done something wrong, you all can call me on it.
My alternator began to fail. Alternator light would come on and flicker out when I turned the ignition on (before starting). Then sometimes it would come on, and eventually it would not come on at all. The battery eventually went stone dead.
Checked the alternator light. Bulb is good. Checked ignition to bulb. It's good. B+ is live. But circuit to D+ is open, dead. Checked it at the alternator. Yea, open, not responding to a live feed (bulb tester). Sounds like a dead alternator, right? Wrong! Thank God.
Here's the skinny, and it surprised me. The alternator base is painted black-wrinkle. Apparently the body of the alternator had a only a tentative ground through this paint. After a while, probably through normal oxidation the stand stopped conducting. Now, see that lonely screw on top of the alternator at about 11 o'clock? :) I put a real ground wire to it.
Alternator light comes on (and off when running), so I'm up and charging, and all is good with the world!
Speedy Jim - I'm okay, right? Do I get a pat on the back or anything for finding this situation? A gold star? Anything?