The battery was near dead the other day. Thought I left the dome light on.

The car's been running a little rough. Today it was idling while I worked on it; it began running rougher; then slowly died. Battery was near dead.

I charged the battery; it started fine. When I removed the neg lead from the battery post it died.

I swapped the alternator (A) with a known good one (B). Same thing. So I brushes out of (A), they were good; I cleaned contacts, replaced and it works great.

I'd forgotten about the exciter wire needing juice to make juice.

Here's the thing: with battery (A) in the car, there was no charging warning light coming on before start-up. With alternator (B) in it, the charging warning was dim.

Now the indicator light works as it should: it comes on with the key on on and goes off after the car starts.

I could have had a bad connector at the battery + post but that shouldn't affect the light. I think (B) has gone bad from sitting and (A) just needed a good cleaning. I just don't get the behavior of the warning light. Unless it wasn't coming on at power-up to tell me that alternator (A) had an open circuit.
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240s: 2 drivers and some parts cars