Check gauges light again

Hi
Vehicle is a 98 XJ LTD, 4.0, AT, Dana 30

I've been having ongoing issues with charging, and holding a charge.
The check gauges light was coming on and the volt meter was dropping to zero, both intermittently.

I replaced the battery, then had the alternator rebuilt from a quality local rebuilder, and it solved the problem. 3-4 months go by , and now it's doing it again.

I charged the battery and got it running. At idle the Alt is putting out about 13.5V, battery tests good with load tester. I loaded the charging system by turning on AC, head lights, rear defrost and stereo. Now the Alt output is down to 12.3V at idle. If I raise the RPM's to 2000rpm, the output raises minimally to 12.5V

What does everyone think? New Alternator, bad grounds, or Regulator in PCM?

Thanks,
Don

Work on ALL your electrical connections with some conductive grease!

Remove the alternator and load test on an alternator test bench. The symptoms strongly suggest the alternator is faulty.

Loose and/or poor quality connections almost always result in the dashboard gauge showing 19 volts.

Thanks. I'll work on it and report back

Update.
I went to remove the alternator, and realized that the 2 nuts holding the field and PCM connector were missing. Because it was almost off anyway I took it into the shop and had it checked. It was putting out 100 Amps. Charged the battery overnight and it was at 12.9V at rest. Put it all back together with dielectric grease and double nuts on the field connector. no-load output at idle is 13.8V. No change at 1800 RPM.

Load it with head lights, AC, rear window defroster, and stereo amp, and it drops to 12.8v at idle, 13.5v at 1800 RPM. Turn the load off and it's back to 13.8V either idle or 1800 RPM.

I hooked up a 12 ga. Additional ground wire between the alternator case and the battery just to see if it would make a difference and no change.

It seems like it's back to normal, but I'm curious why it's not putting out more at idle.

Do you think that the reason it's maxing at 13.8V is because the battery is fully charged.? I know the range is 13.8 - 14.2.

Thanks

Sounds like you found the problem. Alternators do not make full output at idle. Discharge the battery and see if the output rises.