On a 2001 Plymouth breeze how do you tell if the alternator is bad.

You can take the alternator off and bring it to an auto parts store for testing. The battery is going to need to be charged back up. If you have a digital multi meter, you can get the car started, try jump starting it, and check the voltage at the battery. If it is charging the voltage would show at a minimum of 13.8 DCV to a max of 14.7 DCV.