Feel free to correct me if I'm wrong about this, but isn't it possible
that a bad connection is causing the *regulator* to be seeing low
voltage and that it is allowing the alternator to deliver higher
voltages until it reads what it thinks is the proper voltage?

Pete

One thing I didn't mention is that a few months ago my power steering line
sprang a leak and heavily sprayed part of the engine compartment with fluid.
Now that that has occurred to me, I wonder if some power steering fluid may
have leeched into an electrical connector and is affecting the voltage
regulator/alternator.The power steering leak was in the area between the
engine and the firewall and there was very little in that area that did not
get sprayed with fluid.

There is a harness coming out of the alternator that I believe has 4 wires.
When I unplug it, the alternator stops supplying electrical current to the
vehicle.

Thank you to all who have responded.

J wrote:       (1994 Chevrolet Corsica 6 Cyl  155k)

For the past few months the electrical system intermittently surges from 12V
to 19V (according to my voltmeter) at random times.    When it surges, a red
light on the instrument panel that is shaped like a battery comes on.    When
it drops back down to 12V the light goes out.    During a surge the headlights
get very bright and the heater blower speeds up.    I have replaced 4 headlight
bulbs in 4 months but nothing else has blown out.

Sometimes it surges up and down every few seconds, other times I can drive
for hours without it surging at all.  I have never smelled anything burning, nor
have any fuses been warm to the touch.    It does surge more often at high
RPM than low.   However, it sometimes doesn't seem to be affected by RPM.
Sometimes it is fine until I accelerate at which time it surges, while at other
times it doesn't surge at all when I accelerate.

I can not find any pattern to this such as to hitting bumps in the road,
changing temperature and humidity, etc.    I am worried that the car will
become damaged, so I have installed a new battery, a new alternator (that
contains an internal voltage regulator), and new battery cables.    All of the
wires and cables under the hood that are visible appear to be sound and in
good condition.  Can someone please suggest what to look for?
__________________________________________________________________

You didn't say whether the new battery/alternator/cables made any difference,
so the problem must have remained.   If so, I would suspect:

Defective Control Module.     Some alternators are controlled by a remote
voltage regulator in an electronic module.    Your post stressed that the new
alternator has an internal regulator, suggesting that the old alternator did
not.    If so, consider replacing the defective module and installing an original
equipment alternator in the car.   First, try taking the module connector on
and off a few times, to improve the connection.

Defective Voltage Regulator.      This will cause surging, but you replaced the
alternator with a new one which presumably has a good regulator.   If the old
alternator had a remote regulator, that regulator should be wired out of the
circuit.   Take the new alternator back to the parts store and have it tested.

Defective Ground Connection.    A correctly regulated alternator has a peak
output of about 14.5V, relative to its own ground.    A bad ground connection
between the regulator and the battery will cause a voltage drop to appear
across the bad connection, and the regulator will add 14.5V to the spurious
voltage drop.   Recheck all ground connections, especially battery to block
and block to chassis.     Connect a wire from the alternator housing directly
to the battery negative post.   If this good ground solves the problem, it
will confirm that there is a bad ground connection somewhere.

Good luck.

Rodan.