electrical system weirdness

I've got an electrical issue with my 89 XJ, but it's a 4.0, so I'm guessing it would be the same for any jeep. But just in case, here are the details; 89XJ with 250,000 miles on a 4.0. 5 speed trans.
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Anyway, my alternator is not charging the battery. I tried the usual suspects (alternator, belt tightness, ground wire, fuseable link) and all were well (or replaced without fixing the problem).

Then I tried to trace the wires that came from the plug (that connects to the regulator) and I saw that one went into a six-pin connector (physically located right next to the battery) that was old and damaged. I disconnected the plug while the engine was running and I instantly heard the engine go under load, and sure enough, the system was reading just under 14 volts. When I connected it back, the engine kept charging. So I went around like that for a while, and periodically I'd notice the meter in the red, so I'd lift the hood and pull the connector, replace it, and it would be OK for another little while.

Well, then I bought another connector (from a junk yard) and moved the wires connected to damaged ports on the old one to the new one. ... Everything kept charging.

Then I had an issue with my cooling system and in the process of finding/fixing that, I got coolant pretty much everywhere in the engine bay (not pretty... almost got stranded on the site of I64). Well once I got that sorted (a new pump, hoses, thermostat and radiator later) I noticed it was only charging very weakly.

Well, after doing some investigating I have discovered that the first time I start the jeep that day, the systems charges for a few minutes, and then fades over about 10 minutes until it is just barely not in the red on the gage. Then after another 10 minutes it slips into the red and stays there. - If I start it for the first time that day, and then turn off the and restart the engine before 10 minutes, the gage never gets out of the red, even if I only had the engine on for a few seconds.

So I'm thinking it's maybe water related, maybe related to a part that is 20 years old with 250K on it, or maybe just a weird symptom of needing a battery. Since I don't understand how the voltage regulator is supposed to function, or what it connects to, I'm kinda stuck.

Anybody know what's going on here?

My first thought is "regulator" - it's a solid-state back in the back of your alternator (where the black plug goes,) and gets rather warm. With solid-state electronics, heat is the enemy! Apart from needing to keep the regulator cool, Delco alternators are usually quite reliable (you have a Delco CS-130.)

I'd have to look at wiring diagrams to see what goes through that 6-pole connector (I know which one you're talking about,) but I've not got them handy at the moment - nor can I remember where the regulator picks up its "sense" signal on RENIX.

But, that's my first thought.

After I replaced the alternator (and it didn't fix the issue) I pulled it back out and brought it to my not-so-friendly-but-knows-the-deal NAPA guy and he tested and confirmed that the new one was good.

I also have double checked the accuracy of the dash gauge. And tonight I put a new optima in it.... still no change....

bump for the night time crew...

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just to clarify, did you check the battery voltage with a voltmeter across the terminals?