Charging system

I have a 98 5.7 silverado and a less than a year alt and batt. All of the sudden my gauge went from 14v down to 10v. Looked over connections and found no problem. Any other idea's?:screwy:

Have the year old alternator re-checked. Many aftermarket alternators have a high failure rate. I have seen this many times on this forum as well in the field. Use AC-Delco or bosch for replacement.

Have the year old alternator re-checked. Many aftermarket alternators have a high failure rate. I have seen this many times on this forum as well in the field. Use AC-Delco or bosch for replacement.

I will get it checked, but this morning it was charging for about 2mins 14.5v and than went back to 10 or 11v. This has happened in the past but sears just replaced the batt for free cause it was under warentee. I did replace the alt at the same time so maybe it is the new alt again.Man I will be pissed!, thanks for the reply and if you have any other suggestions I appreciate them.

I have a 98 5.7 silverado and a less than a year alt and batt. All of the sudden my gauge went from 14v down to 10v. Looked over connections and found no problem. Any other idea's?:screwy:

Always test voltage and charging at the battery,
The dash Gauge is only a indicater and is not a true voltage gauge.

What is the voltage reading at battery?

Always test voltage and charging at the battery,
The dash Gauge is only a indicater and is not a true voltage gauge.

What is the voltage reading at battery?

Just checked the voltage while running at the batt and was only reading about 12v, so to me the charging system is not working and the NEW alt is now dead! Am I right?

Just checked the voltage while running at the batt and was only reading about 12v, so to me the charging system is not working and the NEW alt is now dead! Am I right?

Right on not cgharging but always test befiore throwing alternator at in.

Check fuse and alt wiring.
Alternators need to be interzizer to charge.
Go over all fuses and make sure you gauge or alt light is interzizing alternator.
Some parts places will test altnator and charging system for you.

Put a load on the system, Headlights,blower fan, Etc. and read the voltage at battery. If it continues to decline then I would expect that the alt is not charging properly.

Right on not cgharging but always test befiore throwing alternator at in.

Check fuse and alt wiring.
Alternators need to be interzizer to charge.
Go over all fuses and make sure you gauge or alt light is interzizing alternator.
Some parts places will test altnator and charging system for you.

What is interzizing mean? I did check the wiring and such and all seem fine.

Put a load on the system, Headlights,blower fan, Etc. and read the voltage at battery. If it continues to decline then I would expect that the alt is not charging properly.

Seems that the alt is not working properly due to batt voltage dropping as assesories were running.Thanks again.

What is interzizing mean? I did check the wiring and such and all seem fine.

For the alternator to start charging it has to have a small amount of voltage from ign or computer or gauge to start it charging.
If it does not have it it will not start charging.
Also check big battery wire on back of alt for 12 volts.

I currently have the same problems with my 86 k1500. Driving me absolutely NUTS! Checked alternator, and found a bad pos post (loose, but worked on tester) replaced it, replace battery (had a concern over ground post on old battery) ran NEW ground cable off battery, to frame, to engine and to cab, and STILL does the same thing. I'll keep an eye on the thread and if I get mine figured out, I'll be sure to let you know how I got it done. This wouldn't affect the tranny shifting out of overdrive would it?

Well the alt though new was bad and did replace with another but this one is a delco and works just fine but now need to get a new batt due to running it down so low. Now when I turn my AC on you can see the drain on the guage my thought is the batt took a beating and can no longer run heavy accessories.

Sometimes the aftermarket alts you get only put out the bare minimum and drop even lower when at idle. If your truck needs a "heavy duty" alt in it, make sure the amp output for the replacement is at least equal to or greater than what in specified, including idle output.

Well the alt though new was bad and did replace with another but this one is a delco and works just fine but now need to get a new batt due to running it down so low. Now when I turn my AC on you can see the drain on the guage my thought is the batt took a beating and can no longer run heavy accessories.


when installing a new alternator because of a long term low charging failure,,,or driving for a time with no alt. operation....the battery must be charged BEFORE new alternator is put in operation....using a NEW alternator to charge a drained battery will greatly reduce its life.....

when installing a new alternator because of a long term low charging failure,,,or driving for a time with no alt. operation....the battery must be charged BEFORE new alternator is put in operation....using a NEW alternator to charge a drained battery will greatly reduce its life.....

Thanks, and again thanks to all for the help!

I've become a firm believer in testing first, and replacing second. If the engine is running and your gauge is low, I'd take the alternator and battery to a parts dealer for testing. Remember that the battery must be trickle charged for a few hours first. If both are Ok, check for proper grounding (I had this problem once on a Chrysler).

Also, I've never had great luck with rebuilt parts. They seem to either fail after several months or work marginally for a few years. I've started going for new parts when available. They're more expensive, but save me from having to crawl under the truck all the time.