Lights cycling bright / dim

When idling, headlights are fluctuating from normal brightness to slightly dim. Ammeter shows the same cycling, staying on the positive side.
Any idea what could be causing it. Engine RPM is staying constant, not
cycling.
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It's probably the alternator, just went through that myself.
I have a 97 Lincoln Mark VIII and back in the spring I noticed it on the dash lights (speedo/tach) more than the headlights, but those are HID's on mine.
Around the 4th of july it started squealing a bit and ended up replacing it a couple weeks ago, just before labor day.
No more strobing/fluctuating on the lights and quiet as a mouse.
For it's worth, although the car has 3 different warnings for the charging system, the batt light, the info center printing out "check charging system" and/or "low batt voltage", none of those came on once.
Mine was a 4G 130A type, rather expensive from even Autozone/Advanced but here in Chicago we have a number of rebuilders, only ran $103 plus tax, 1 year replacement warranty.
-bruce snipped-for-privacy@ripco.com
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Thanks a lot, Bruce! Especially the tip to look for a rebuilder. I replaced the same alternator on another car and it was over $200 best I remember - definitely more that I expected.
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On Wed, 16 Sep 2015 10:14:47 -0700, "Snuffy \"Hub Cap\" McKinney"

When my Alternator seemed to be acting up I called a rebulder I use for info. He said it could be as simple as corrosion between the aluminum block of the engine and the aluminum casting of the alternator interfering with the ground connection. He also said it could be some lose wires inside that commonly cause trouble. Also that a weak battery can make the alternator seem bad. I pulled the alternator and took it in and he took it apart, found no internal problems, tested it and found no problems on his tester. In the meantime I put the battery on the charger. I put the alternator back on and it seemed fine. I load tested the battery and it was weak so I hauled it in while it was still under warranty and got a new one. Have not had any problems since.
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remember - definitely more that I expected.

I learned the hard way (and keep forgetting and learning over and over) to check the easy stuff first. I have had several problems over the years that turned out to be bad ground connections.
Last year I was not getting circulation to the heater core and a radiator shop said it was the valve. So I bought a new valve and installed it without thinking anything about it. Still had the problem, and turned out to be a leaking vacuum hose. So now I have a new valve and a spare....
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