Maybe check the alternator

I just went through this on my '95 Monte. Mine turned out to be bad
connections at the power distribution block.

First thing I did was test to see if the low voltage was system wide. I did
this by checking the voltage at every fuse and isolating which ones were at
the low voltage. Only a few were at the lower voltage and others were
normal. The voltage at the battery was also normal. This lead me back to the
power distribution block beside the battery. I took it all apart, cleaned it
up and all is like new.

Here's a link to the thread:

http://tinyurl.com/d2qnp

Steve

Try checking the voltage right at the battery. With the engine at a fast
idle and no accessories, then at a fast idle with headlamps on and the
heater blower on high. If you need a meter, Harbor Freight has them for
around $4.00 on sale. There are more tests to make but start with these. One
seemingly obvious thing a lot of folks miss is the belt. It has to be tight.

Al

Other than I'm lost. Any help?

Check your ground...from the battery to the frame.

    Before changing another battery or alternator:
Clean the terminals.
Check the pig tail from the distributor for damage or a lose wire in the
connector.
Get 'em warmed up, and take a trip to a autoparts store that has a
battery & alternator in vehicle load tester. Have it checked. Have them
run the test a few times try different accessiories.
Charles

   

I had a similar problem on my 95 5.7 K1500 trailer towing package several
weeks ago.....was getting low voltage and had a leaking battery terminal.
Replaced the battery and the starter went out the next day, don't think it
was related as I just replaced it 6 wks before (200,950 miles on the
original starter!), just a bad rebuilt starter. Anyway, replaced the
positive battery cable that goes from the battery to the drivers side
firewall distribution box as it was corroded from the inside from where the
battery had been leaking into it. The trailer towing package has two
positive leads that go to the positive side of the battery. One goes to the
starter and the other goes to the firewall distribution box. Cleaned all
connections and still had the fluxuating voltage. Would crank right up first
in the morning then later wouldn't crank at all, would just click. Would
tighten up the battery terminal, and would work fine for a little while and
start the whole process over. After overtighting the terminals on two
batteries and causing the positive side side mounts to come out we found out
what the problem was. The lead spacer that goes between the positive side
cables to the positive side post of the battery had been squashed down to
less than a 1/4 inch over the years. I put in a new spacer, it is like a
half inch or more in thickness and now that has fixed all of my electrical
problems. What was happening with the old spacer was that when I tightened
down the terminal on the positive side the long battery bolt would go thru
the side mount bung and poke a hole thru the battery. Thank goodness for
O'Reilly's liberal battery return policy, as it took two batteries to
discover what the problem was. Now both the terminals are good and tight and
I get a solid 14 volts in the middle of the voltmeter all the time now. This
is a little long winded but hopes it might help someone out there......Mark

This is normal. Believe it or not.
The alternators are set not to deliver full power at idle so they will not fail in hot weather.

One way around this is to get a smaller alterantor pulley. Since you changed the alternator, you may have gotten a larger pulley by
mistake.
You can calculate the rpm needed, then using the diameters find a smaller pulley that will help.
Dont go too small, as the alternator may then fail because it will be subject to higher rpms are higher engin speeds (4500 rpm). I
believe 8000-9000 rpm is the upper limit.

Another approach is to replace the alternator with a larger unit, such as those used on police and fire vehicles.
http://www.wagneralt.com/

And if your savy, you can experiment with different mfgs' voltage regulators, this worked for me.

Good luck