Indeed, with today's gas prices and 15-17 mpg, who can afford to pay a
mechanic? Or even to drive at all? That's why I parked my Explorer in the
garage and re-commissioned the long mothballed 21 year old LTD. No ABS, no
airbags, no dual-media entertainment system, and the headlights don't turn
on and off on their own; but boy, that obsolete throttle body injected V6
and three speed transmission are still happily delivering an astounding 19
mpg!

Don't know much about Lucas oil products. Electrical products by the same
name have a spotty reputation, but I have not heard of any of those ever
being used in an Explorer... So before we pull out the chart, let's figure
out if this is just the gauge, or the voltage is actually flickering. The
simplest way to tell might be parking at night in front of a wall, taking
your foot off the accelerator and observing the headlights. If the lights
are bright and steady, you can probably leave your vehicle parked right
there and go to sleep peacefully, as there is little to worry about (unless
you are a perfectionist like me, and want every gauge to work in a 15 year
old vehicle with over 200,000 miles).
The other crucial piece of information that you kept secret from us is
whether the engine is idling steadily or not. If it idles poorly, the
voltage will be justified in doing what it's doing and you need to take care
of the idling.

And no, it does not rhyme with 'altimeter'. The word is 'voltmeter'.

It seems to flicker like a stereo equalizer

It's "voltmeter".

This reminds me of a maddening problem I had with a Ranger which was
much like this. I traced an intermittant short thru the wiring harness
to the cigarette lighter/ashtray. I don't smoke, so I throw change in
there. I had left the lighter out of the socket when plugging something
else in, and a penny had slid down into the lighter socket- It didn't
make good contact, so it didn't blow the fuse or smoke, but the
vibration at idle would cause it to jiggle and intermittantly short. It
did make the voltmeter needle thrash around.  So it could be something
like that- anything that intermittantly draws a lot of current. You
could pull fuses a few at a time to see if you can isolate it to a
particular circuit. Suppose you pull the dome light fuse and the
problem goes away. Look for a pinched wire or other similar problem in
that part of the wiring.

More info would help- does it crank strong? Does the battery hold a
charge if it sits for several days? Do your brake lights work
correctly?
-Paul

My first inclination would be to wiggle test the harness/connectors involved
in the charging system while an assistant watched the lamp (engine running,
of course). Spread connectors, corrosion, previous repairs or
modifications.... these are just some of the possible causes.

I have found no crankcase oil additives (and few other additives) worth the
expense. Nothing beats timely maintenance and repairing small concerns
before they grow into budget busters.

As for additives.... I'm reminded of a quote I once heard.... "I you build
it, they will come...." (we could follow that up with P.T. Barnums "There's
one born every minute..."). As for repair and maintenence, I have my own
quote...."Cheap ain't".

testing...