Q: 2012 chrysler 200 won't start after replacing alternator which was bad after testing.

Hi there. It sounds like something may have shorted during the alternator replacement. If the positive cable going to the alternator made contact with anything metal, then it may have blown the main fuse. If not, then the battery should be checked to see if it has low voltage. If the battery is also fine, then the low voltage that was in the system may have corrupted the programming in the computer, which will affect how the module communicated and starts the vehicle. I usually use a computer scan tool to clear the computer and then reboot it. From there, each Check Engine code can be diagnosed one-by-one to pinpoint the related faults. If you need to have this checked out, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose your starting issue and thoroughly inspect your Check Engine Light in order to make the correct repairs.