I have a 2003 Chevy Cavalier. I just put a motor in it that only has 55,000 miles on it and I bought a used alternator and battery. I had the alternator tested and it was good, it put out the right voltage. However, I have to jump my car to start it every time still and when you jump it it will only run for about a minute once the cables are unhooked and then it will die. Also, as soon as the cables come off the battery light comes on. What could be the problem?
Even if the alternator and battery are good, if a wiring circuit issue to or from alternator, you still have a problem. Make sure the battery has a full charge, if the battery is down, you cant do any testing. Dont charge the battery off the alternator.