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
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.
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.
replaced the same alternator on another car and it was over $200 best I
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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