Charging issue

[nickl011]

Not sure if this is the correct place to put this, but here goes. Now the alternator in my Tahoe had, what I believe, a bad voltage regulator as the volt gauge on my dash would wage back and forth over 14v and cause my lights to flash. I bought a used one off a member here and put it in today. For the first 10 minutes that the truck was running after I got done switching them out, the voltage gauge stayed just one tick over 14v, and didnt wage like it used to do and didnt flash/flicker the lights. Even with my subs turned up and my lights on, the needle never moved. But after taking the truck for a short test drive through campus, I notice the volt gauge drop to 1 tick over the 9v mark and the battery light came on. I turned my lights off and pulled the fuses on my amp and it didnt change anything. Im just curious as to what anyone might think is wrong.

 

[sewlow]

How old is the battery? Could be on it's way out. Any parts store can test both the alternator & your battery for you. Get the first alt. tested too. If the second one didn't clear up your problem, it may be bad, too, or it wasn't the problem in the first place.
Check & clean all your grounds. If they are really corroded, the internals of those wires are probably just as bad or worse. Check those with an ohm meter. A little too much resistance over a series of connections adds up to a bigger load that the alternator has too push the charge through. I'd replace 'em if they are the originals or just old.
You have more than one sub, so it sounds like you have a pretty big sytem in your truck. Have you gone overkill on the power/ground wires for that, or just what it requires? Done 'The Big Three'? (Due to the way the site is displayin for me right now, I don't have the search option, so that I can find the thread for that upgrade for you.)

 

[nickl011]

Battery is less than a year old. My buddy stuck my multi meter on the battery at the disconnected neg battery cable and the still connected positive cable and it read 12.5v. I have two 12" rockfords with 200 rms at 8 ohm impedance, the amp I believe is a 500w 4 channel bridged. Power and ground cables for the system are I believe 4 AWG. I have not yet done the big 3 but it is on my list. I pulled the fuses on my amp so the subs arent hooked up. I will see about testing both alts, IDK if auto parts stores can test an alt while its still in the truck or if the have to be out for a bench test.

 

[Marcos]

I used to work Parttime at autozone and we used to test them on the car, just be sure the battery is fully charged before getting there or the scanners won't let you test the alternator.

 

[nickl011]

Swapped the alternators back. The original one work just like it should! Holds a charge at a little over 14v, no wagging volt gauge or flashing lights. I decided to switch them back after I notice the voltage gauge slowly going down until it got into the orange area on the gauge. Took the used one I just bought to NAPA, they bench tested it and its shot. No DC voltage coming out of it.