*under charging the battery- cause by bad ground/ loose or poor connection- loose or broken belt--- these will all cause the car to run either soley or primarily off the battery. when the voltage drops to 12v DC or below, all the lights on the dash will light up along with the "battery light." the brighter the battery light the less voltage the battery has. if the voltemeter drops momentarily when you put a load on the battery (hit the brakes primarily) then this is/can be an early warning sign of a altenator on its last leg.
*over charging the battery- faulty voltage regulator, regulator contain inside the altenator. must replace the altenator to fix.--- if the voltage gets to high it turn your electronics into burnt cheese. warning signs would be the voltemeter on the dash reading abnormaly high. also if you have a radar detector pluged into your cigarette light it wont come on.
the altenator should be putting out between 13.8v and 14.2v DC. i am not sure how you tested it but if you only tested the terminals on the battery it will only read 12v. you can take your car to auto zone and they will test if for free and it only takes a sec. they will also be able to identify any problems that it is having and tell you how to fix it.
I was a bit confused by your post - did you say you had it tested at autozone?
If you haven't had it tested it wouldn't be a bad idea to run it down to your local parts store and have them test for free. If you get a new one, have them test that one before you leave the store. They sometimes defective out of the box and you might as well save yourself a couple of hours.
Replacing the alternator isn't too bad - just getting the belts off for the first time that is a [email protected]#$. After you've done it that first time you know all the trouble spots!
Alternator is not hard to change. Just put the front end up on ramps. Use a 14mm socket to remove the four sway bar bolts. The sway bar drops down. Lossen the tension on the alternator belt. I took lose the coolant tank bolts to make it easy to get to the top two alternator bolts. The coolant and tension bolts I think were 10mm while the alternator was 12mm. It is very easy. It should only take about 1-2 hours to complete the job if that.
i got the Alternator yesterday and it was the wron 1 they sold me.....tottaly different type of pully and it was way larger...but i took it back and got a new 1 from another place ....and it seems to be working, but my speed gauge cant decide weather it wants to be on or not....