My XJ eats alternators

I have had my 99 xj since 2001. Since then I relplaced the alternator twice and I can tell that its coming around for a third replacement. It seems to happen every 20k miles or so. These are the symptoms:

Guage cluster goes on and off
rough idle
volt meter starts dropping below 14 when the vehicle is rolling down the highway.

Any ideas? Is anyone else experiencing this?

Are you getting mud in it?

check for bad or loose connections
a bad ground to or from the alt. can lead to failure

Are you replacing it with an autozoo/pep boys/auto parts who knows alternator. All your high vol. auto parts houses use UPC corp (Unit Parts Corp) for remans and they are less then good.. Napa ACDelco or BeckArnley are the only ones i would use... A store mgr at Discount (now advance) auto parts was telling me that they buy their alternators at something like 8 bucks an alternator remanned... They buy them with no warrenty and self insure them.. THats why most will test the alternator before it leaves the store and test all their returns... i have never had a Napa ACdelco or BekArnley fail on me

That's why I don't arse around with chain stores for anything more complex than fluids and - maybe - filters. Wherever possible, I'll deal directly with the rebuilder.

Check out my website - I've never needed Rod's warranty, and I've used dozens of his alternators and starters. The only time I've needed to buy another one is when I buy another vehicle, or work on one for someone...

5-90

I haven't gotten mudd in it. Its basically a city driver. I'll check the connections and the ground. Thanks for the tip.

Experienced something similar this morning in my 99... not sure of alternator age since I've only had it over a year now. The gauges & headlights dimmed & the "check gauges" light came on while driving down the road (was only running about a minute or so). I turned off the heater fan & the voltage came back up & things returned to normal.

I'm in PA and yesterday was our first snow. I figured maybe something with the humidity/precipitation/temperature caused the alternator to act up or altered a loose ground.

When I got home from work today, I removed both battery terminal connectors & cleaned the posts & connectors really well. I was getting a solid 14.1v, 14.2v while it was running(checked with my multimeter). Hopefully it was just a temporary thing, but after checking this thread I fear that the alternator may start acting up.

The ground to the left of the battery on the fender seemed fine, is there any other ground coming from the alternator that I might check?