My alternator went bad I changed it with one from autozone. The problem is I put the tester in and its saying that its not charging properly its 12v, when the car on. I went back to autozone and they tested the the alternator and it passed. What else can be wrong with the car, that its not charging properly.

 

Check all electrical harness to make sure it's not melted, esp the harness connecting to the altenator. Also, see if the battery is charging. You may have a bad battery.

 

bad battery..... does it crank fine?