Hey CL. I'm having a problem with my charging system. The car died on me 4 months ago, and I put a new battery in. The alternator ended up testing bad so I replaced it too. The car drove fine for 3 months or so. One night the car died again while driving. Battery tested good, and alternator tested dead so I replaced it with a warranty replacement. I took the battery to get charged at AutoZone, and they said it didn't take a charge. I took it to Napa, and oriellys for a second opinion, and they claim the battery is good, they even tested for a dead cell. Can anyone suggest a next move here? Could the battery be bad, yet test good? Battery is 4 months old, and the new alternator is 1 week old. All connections have been triple checked, and chassis ground is solid. Thanks in advance for the help.

 

What kind of alternator? Did you belt check tensioner? Mine had similar symptoms (and noise) when mine was bad. I replaced everything as well.

 

Alt is a Napa premium replacement. The tensioner seems fine, keeps plenty of tension on serp belt.

 

Ok. Output voltage at the alternator post was reading around ~10v and dropping. Is this new alternator dead, or could there be another reason why It wouldn't be charging?

 

Alternator should be putting out near 14volts. If you are getting near 10volts alternator isn't working properly.
Should be able to get a new replacement alternator.
As well as battery if it has a dead cell.

 

Ok. New alternator in, and dead cell test done at Napa, orielly, and AutoZone and all show good. When testing the output of the alternator, it showed 14v right off the bat. Tested it after running a few minutes and it tested at 0v, and the needle on my multimeter just shivered. I turned the car off, checked all connections, and everything looks good. Started it again and it read 14v over and over. I took the car up the road, and back and can already tell it's not getting the right power. The starter makes that clicking sound they make when starting with low power. It's too late to test voltage tonight. WHAT GIVES??? I'm lost here guys. Any help would be greatly appreciated. Does anyone have a good wiring diagram for the auxilary plug on the alternator? Anything else I should be looking into? There is no excessive draw on the system, and nothing else about the car has changed.

 

I feel like if I were to continue running this, it will likely do what the last 2 alternators did and just die on me. What could fry an alternator, before the battery dies, over and over?

 

I have had such trouble searching for this because nobody updates their threads once their problem was fixed. I figured I'd update this with my results.

I ran the "big 3" upgrade, power wire from battery to alternator, ground from negative on battery to chassis, and chassis to engine block ground. I left my original alternator wiring in place, and still had issues with the alternator not supplying proper readings. This was a tested good alternator and battery. I tested for excessive resistance in my grounds, and everything checked out. I decided to pull the original alternator power wire(thats actually 2 wires wired to a single ring terminal on each end) from both the alternator and the fuse box, so I was running solely on the new wiring I had run. Suddenly the car seemed to run much smoother, but the idle would drop low and volts would drop slightly again.

I had checked timing every time I replaced an alternator, and it read fine, but once I had that original power wire replaced, the timing was a bit off, and the idle was low ~200rpm or so. I re-timed the car and now everything runs smoothly. No drops in power, perfect idle, etc.

Long story short something in my wiring appears to have been the problem. Not sure if it was corroded, shorted, or what but replacing it was very easy. I even heat shrinked all the new wiring so it looks OEM in the bay. If you're having charging issues, the "big three" upgrade is a solid investment.

 

so I was having all of these issues on my 97 SC300, changed the alternator with an as close to OEM replacement(not refurbished), brand new battery from autozone, still had the same issues, car would run and drive for about 15-20min, I checked all the wiring, deleted the aftermarket car lock fob the previous owner installed, and I’m left with one last option, there is a fuse linked in between the power line from the battery to the alternator and if that is blown then even with a good alternator it will not charge the battery, it’s a 100amp fuse within the fuse panel under the hood, you will have to left up the fuse panel to unscrew it in order to replace it. Good news is the fuse is less than $10 at autozone. My buddy has an 02 IS300 and said he had a very similar sounding issue, once he replaced that fuse the problem went away, will update tomorrow if that fixes my problem but I just don’t see anything else that could be causing it.