alternator woes

[Jesaire]

Hi all, first let me thank all you mechanics who give back to the community, I am not a certified auto mechanic but i understand the mechanics of it as I am an Hvac tech.
Recently my 05 sub LT has displayed flashing instrument panel lights, I noticed the alternator fluctuating from 8 volts to extreme 18 volts, I replaced the alternator and the problem appeared to have been solved. Well about 3 weeks later I am getting the same events, hi to lo voltage it's either one or the other.
Can someone help with what I should test for now? Could it just be a bad alt again.?


Thanks in advance
Jesaire

 

[Spriteman]

It sounds like you might have a grounding problem. If the battery is not getting a good ground it will make the alternator work too hard.

Clean all of the grounding points and make sure the battery terminals and wires are really clean - don't just clean the outside - make sure you take them apart if there are multiple wires clean all of it and then reassemble. Use some cable protectant when you're putting it back together.

You can have the alternator rechecked at an Autozone type place - their tester checks the battery, starter and alternator.


Here's a link to a wiring diagram for your burb - I think it's the right one - http://parts.nalleygmc.com/showAssembly.aspx?ukey_product=2778890&ukey_assembly=369908&ukey_make=1024&ukey_model=14543&ukey_driveline=6218&ukey_trimlevel=14209&modelYear=2005

 

[Jesaire]

Sprite man, thanks I might be overlooking the basics it great to always get a second set of eyes on a fix...
I will give it a try

Jesaire

 

[Chuzz]

Where'd you get the alternator? If it's an Autozone one, it's not uncommon for it to be defective out of the box. I used to work for them as a PSM and asst. mgr. I saw a LOT of alternator and starter returns after a few days of installation. It got so bad when I worked for them, that I wouldn't sell either one without bench testing it first. And that doesn't always work, because you can't put a full load on them by bench testing. Do what Spriteman has suggested because they're great suggestions. I'm betting it's a crappy alternator.