Alternator / regulator? Something's failing, need some advice

1992, XJ, 4.0L, AT, ~173k

Charging system intermittently fails, ie runs off bat at 12v. On a 1hr drive for example, I might be at 14v for a while, then I'll look down and notice I"m at 12v, I'll keep an eye on it and eventually it will be back at 14v again. It has been going on for a while now, but the problem has gotten worse as it is more frequently not charging now than it was previously and I've run my battery down.

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1- If it was a grounding issue, I would be overcharging not under, right?
2- Is the regulator internal to the alternator? Could a failing regulator exhibit these symptoms?

TIA

I had exactly the same problem. Time for a new alternator. I just charged up my battery every day and drove it with almost no alternator for a few months.

Concur. The regulator that ChryCo built into their PCM is, fortunately, fairly robust (although I still prefer the Delco CS-series - if the regulator goes out, you can replace it without changing the whole damn engine computer.)

This may be a good excuse to uprate your alternator - if you'd like options, click the link in my sig and pillage away!