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.
...
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?

I would start at the beginning...first charge and check the battery. If that is good, check the alternator by full fielding it...do this by finding the field wire and grounding it (field wire is one of the little ones that go to a two wire plug at the back of the alternator...unplug it and the one without voltage or very low voltage is the field wire). When you connect the corresponding field terminal on the alternator to ground with the engine running, it should begin charging. If it doesn't, the alternator is bad. If it does, keep moving back up the wire and doing the same thing until you find the break in the wire.

If there isn't a break in the field wire, it could be the regulator or the positive wire. Check the positive wire wit a volt meter. Check it at the voltage regulator for full 12+ volts and keep checking it all along; at the plug and at points along the wire.

If the positive wire is also good, sounds like the regulator. I don't know for sure, but I believe the regulator is in the computer module. If it is, the module grounds and voltage should be checked before replacing. If all that is good, replace the module ($$$:eek:).

edit: I would do all this methodically because it sounds like the coolant may have damaged something besides the suspect plug

I pulled the Alt and brought it to NAPA (where I know the guy there has a clue) and it tested fine. - Actually it was the second Alt I brought there... the first thing I did was replace that (the first had a really bad squeek, so I wanted to replace it anyway.)

I bought a new Alt, and when it didn't fix the problem I had it tested. So I'm pretty comfortable it isn't where the problem lies.

bump for the evening people

last bump