[Vwdiesel] more alternator questions

[George Allison]

OK, I'm attempting to chase down some really weird issues on my '76
Volvo 245, and realized that my brain is not equipped with the
knowledge to capably deal with this problem. I know this is a non-VW
item, but I figured if anyone could give me a clear, quick overview of
what might be possibly causing this thing, they'd be on this board.
Maybe it'll be an educational experience for all of us. :) This is
kind of a long story, so bear with me.

A month ago I dragged this car out of the Pacific Northwest backwoods,
where it had been sitting and rotting for a year and a half. It's got
241,000 miles on it (gotta love old Volvo redblock motors: great oil
pressure, no smoke, and excellent compression!), and had only been
parked because a fuel hose went bad. I replaced that and the car fired
right up. I started to drive it the 25 miles back to my house, and
when I was about 4 miles from home I noticed the fuel and temp gauges
starting to drop, in unison. I pulled off the street and turned the
car off to check things out. It was very hard to restart (slow
cranking). I got it going again, and almost made it home, then a few
blocks from the house the engine started to sputter and died. I tried
to restart it, and got nothing at all.

Now, here's where it gets strange: during all of this, the amp light
never came on to tell me that it was not charging (which it definitely
wasn't--if I charge the battery up, start the car, and check the
voltage at the battery now, it's about 9.8v). In fact, the amp light
NEVER comes on, even with the key on but the engine not running. I
know it was charging when I first got the car running, because I drove
it around extensively for a few days on Vashon Island (where I got the
car), and it ran well, had steady/accurate gauge readings, and
performed many successful restarts. Unfortunately I don't remember for
certain if the amp light was working properly at that point, but I
seem to recall not. The alternator was replaced (rebuilt NAPA unit) by
the previous owner about 6 months before the car died, and only has
about 1000 miles on it. Battery is known good.

This car has the older-style external-regulator system. I replaced the
regulator, and it changed nothing. The Volvo system excites the
alternator through the amp light, and I know that circuit is working
because I get 12v at the end of the exciter wire when the key is on,
and the amp light comes on when I ground that wire against the block.
All I can think is that this means something broke inside the D+
circuit, and the alternator is now unable to excite or to turn the amp
light on? This would be a strange death (all the others I've
experienced have shown the amp light when they died, indicating low
charge), but maybe it's possible. Anyone ever experienced this, or
have anything relevant to relate? Is a new alternator the only fix?

Thanks in advance,
George