99 Blazer Charging problem

99 Blazer 4.3 V6 not charging battery- Autozone tested alternator and said it had no output, so I replaced it. Still not charging battery, so I replaced the battery, and removed the new alternator had it tested at Autozone and it check fine. I cleaned cables on battery and alternator. Any ideas would be greatly appreciated.

Sometimes battery leads will rot from the inside and you would never know it from looking at them or handling them. Battery leads are cheap and a clear afternoon is all you need to get them swapped out. If you are confident in your own abilites to swap a battery and alt out by yourself, you can do the swap on the cables, easily. While in the battery/cable acessories section, pick up a new alternator pigtail too. Cut the old one off and splice the new one in with a good crimp. You'll be running like a champ then.

Make sure that your battery is fully charged before you take a test start and drive. Putting a half cranked-down battery on a new alternator will shave a year clean off it's lifecycle!

See if you have power on the heavy red wire going to the alternator. There is a fusible link between the battery and alternator in that wire. The VCM actually controls the charging. You will need a scanner to check the VCM.

I checked for continuity from the positive battery cable to the heavy red wire going to the alternator. Checked ok, I gave my battery cables a good look over and they seem fine. I removed the boots off the battery and alternator cables and cleaned them well when I replaced the battery the other day. But I will look at replacing these cables possibly this weekend sometime. Also it does crank and run, just not charging the battery. And do you know if autozone can test the VCM and what is the VCM? Tks.

VCM = Vehicle Control Module In some years also known as ECM, PCM depending on the systems it controls.

99 Blazer 4.3 V6 not charging battery- Autozone tested alternator and said it had no output, so I replaced it. Still not charging battery, so I replaced the battery, and removed the new alternator had it tested at Autozone and it check fine. I cleaned cables on battery and alternator. Any ideas would be greatly appreciated.


did you reconnect the small 2 or 3 wire connector to the alternator?

if so, check that part of the harness, continuity check it too.

Here’s an update.

I took the car to the local dealership because I was worried about the wiring. My neighbor had a blazer that had a wiring problem and it burned up and since this is my wife’s car I didn't want to take any chances. But it turns out the alternator I got from AutoZone that they tested as good was really bad. So I spent $85 for the dealership to tell me I bought a bad alternator. But at least now I know my wiring and PCM is good.
Also you can't all ways trust the alternator bench test at AutoZone and they will test it before they replace it. So you may have to get mad demand they replace it like I did.

Thank you all for your help.

Yea, that did sound funny.

Good to see you are good to go.

Now you know that even new parts can be defective.