Alternator: How to check if its Bad?

Can anyone tell me how to see if the Alternator is no good in my blazer. I am having problems starting it. I changed the battery cause it was old and it was having trouble starting. i still having the same problem. I read some posts and I have some of the same problems others are having. The fix seemed to be the alternator. When i go to start it all power is lost. When I pop the hood or beat the crap out of the steering wheel the power sometimes comes on. Then soemtimes I got to jump it. I had a post going about this and I figured I fixed it by cleaning the the cables and checking all the contacts. So i starting to lose it. So before I do :) I am gonna try to test the alternator. So if anyone can tell me how to check it that would be nice and save me from blowing the blazer up.

Try licking it!


No seriously, Autozone can check it for you for free. Or any repair shop with a good battery charger. My battery charger, when hooked up can tell you if the starter/battery/alternator is good/bad.

Check the battery voltage when the engine is running and see if you are getting 14.4+ volts out it for starters.

Turn your headlights on after dark, but before you start it.
Start it, and if the lights get brighter it's working

Use a real voltmeter , NOT the one in the dash . Check the voltage on the battery when engine is off. Then crank it , Check the voltage while the engine is running , the voltage should be between 13.5 and 14.5 volts . DO NOT try disconnecting the battery while the engine is running to see if the alternator is working . While the engine is off , check the wire and harness on the back of the alternator for corrosion . It will cause a voltage drop and keep the battery from charging correctly . Rob