I have a 94 C1500, 350,auto that runs on low voltage with lights and a/c on.

Engine idling with no lights or a/c, no problem, shows 14 volts on the
factory gage.

Engine idling with progressive amounts of load, a/c, low, med low, med hi,
high, then headlights - and the voltage progressively drops to usually to
about 10. Running at highway speeds, this usually comes up to about 12.

Never a problem starting, but headlights appear dim.

Alternator is second new one in the past few months, little difference with
the second which declined to a little worse after 500 miles or so. Battery
is 3 years on a 5 year batt, and fill levels are normal, and terminals are
clean.

Did I get two bad alternators in a row, or is there something else I could
check?

On Sat, 15 Aug 2009 01:21:49 -0500, "Tim" <beevis (AT) snotmail (DOT) net> wrote:

I have the same problem with my 92 Safari 4.3. But it has a digital
gage set. And most don't work. It could be the gage is off. My engine
runs fine, but my gages indicate it is overheating with no oil
pressure. The speedometer and the odometer, are the only ones
functioning.
Try a volt meter. It could be a cell is going in the battery, or the
headlights could need replaced.

<4546 (AT) mydaja (DOT) com> wrote

I didn't realize old head lights would do that. I'll swap them out and see
what happens.

I think you need to check voltage across the battery terminals at hi idle
with everything on. If you only have 12 volts and not 13.5 to 14.5 V, you
need to replace the alternator. Make sure your belt is tight.
Headlites don't need replacing if they aren't burned out.
Good luck........Pete

Tim wrote:

I have a 99 for work I had the same problem with for years. I run
flashing lights and CB all day long whether or not the truck is running.
I was going through a battery almost every year. They just got weaker
and weaker. I replaced three alternators. Always the same thing.
Would start out over 14 volts, but after a short period of time, I
couldn't run much without the voltage dropping. Finally I purchased an
alternator from a different source. Now I get steady 14 volts again.
The battery holds charge and strength just fine. The weak alternators
were causing all my problems. Never occurred to me the cheap part (made
in Mexico) would be bad. I had three in a row. Unfortunately, I can't
recommend where to go, cause I don't remember where I bought the good
one. Just wanted to say I think you can get crap alternators brand new.

"Pete" <kc5gxc (AT) isp (DOT) com> wrote

I'll do it Pete, that would be the most logical answer. I had this problem
years ago with a old Toyota pu, and it turned out to be a problem with the
wiring harness. So I though I would check around, perhaps see if there was a
problem area on Chevy truck around that period or something. But it does
indeed seem to be an alternator problem.

"sticks" <wolverine01 (AT) charter (DOT) net> wrote


You might very well be right, Sticks. I have heard a lot of guff about
AutoZone rebuild items, but my mechanic always insists on them. I know I'm
not crazy about the power steering pump they sold us. It doesn't work any
better than the old one, but it doesn't make any noise.

I'll test the battery voltage with a Fluke, and that seems to check out,
I'll just have to try another alt. from a different source.

On Aug 15, 1:21*am, "Tim" <bee... (AT) snotmail (DOT) net> wrote:

First of all Get a good Digital voltmeter you can get them at auto
parts stores don't be cheap. Run the engine and connect across the bat
terminals and verify the reading on your dash gauge is correct. It
should be from your description.
If it is then make sure your battery is good. Have it checked and
replaced if necessary. Once a good battery in installed see if you
problem is better. If it is only improved or not better then problem
is in the alternator. Yes they can fail right away if you load them
too much the diodes get hot and leak current which means no charge the
hotter they get the less charge you will get out of it. Eventually
they fail. Delphi Alts are not too good.
I have a 99 suburban it came with the small Delphi 105amp alternator
it lasted 40K here in Austin.I bought a new one but I noticed also
that it could not keep up with the AC and such at idle. Lets face it
this is a very poorly designed system, small Alternator thin charge
wires ect. I added an electric fan to the condenser for better cooling
and the Alternator could not keep up with the extra load. The cure for
me was to just upgrade to a 140 amp alternator. It fits right on the
brackets but is bigger so I had to make a back bracket for it for
extra support. The plug on the side of the Alternator is different so
I had to hunt around and get one from a alternator shop. GM wanted $50
for it and on mine only one of the 4 wires is used.
I also had t change the belt since this alternator is bigger. I did
add an additional charge wire too since the original wire was too thin
of a gauge for this application.
Now My Volt meter is always 13.8 to 14.4. Even with AC full on the fan
motor never slows down when I stop at a light.

The total cost was about $160 for everything. But mine is a 99 and
yours may be different.Could be cheaper too.
If you decide to just replace yours, always pick a good new one, it
does not have to be a GM since we know some of them are not too good.

good luck

"jg9100 (AT) gmail (DOT) com" <joe.goodart (AT) gmail (DOT) com> wrote

First of all Get a good Digital voltmeter you can get them at auto
parts stores don't be cheap. Run the engine and connect across the bat
terminals and verify the reading on your dash gauge is correct. It
should be from your description.
If it is then make sure your battery is good. Have it checked and
replaced if necessary. Once a good battery in installed see if you
problem is better. If it is only improved or not better then problem
is in the alternator. Yes they can fail right away if you load them
too much the diodes get hot and leak current which means no charge the
hotter they get the less charge you will get out of it. Eventually
they fail. Delphi Alts are not too good.
I have a 99 suburban it came with the small Delphi 105amp alternator
it lasted 40K here in Austin.I bought a new one but I noticed also
that it could not keep up with the AC and such at idle. Lets face it
this is a very poorly designed system, small Alternator thin charge
wires ect. I added an electric fan to the condenser for better cooling
and the Alternator could not keep up with the extra load. The cure for
me was to just upgrade to a 140 amp alternator. It fits right on the
brackets but is bigger so I had to make a back bracket for it for
extra support. The plug on the side of the Alternator is different so
I had to hunt around and get one from a alternator shop. GM wanted $50
for it and on mine only one of the 4 wires is used.
I also had t change the belt since this alternator is bigger. I did
add an additional charge wire too since the original wire was too thin
of a gauge for this application.
Now My Volt meter is always 13.8 to 14.4. Even with AC full on the fan
motor never slows down when I stop at a light.

The total cost was about $160 for everything. But mine is a 99 and
yours may be different.Could be cheaper too.
If you decide to just replace yours, always pick a good new one, it
does not have to be a GM since we know some of them are not too good.

good luck

--------------------------------------------------------------------------------

Thanks, I have had suspecisions about the battery, but it checks good at
rest. I do have another battery I can try, might not hurt.

I'd recommend a good analog meter, instead. Analog meters are
better for some troubleshooting because they are quicker and
don't show transient fluctuations as readily. Though, having
both is a better option since a digital meter comes with more
functionality out of the box than analog. Check Lowes or Home
Depot for digital meters. Hit Radio Shack for the analog.

"Tim" <beevis (AT) snotmail (DOT) net> wrote