1998 Malibu pulled installed new ignition cylinder and now car attempts to start
 

Old igntion would not turn, pulled ignition and separated the black plastic housing from the back white housing. Removed old cylinder lock and installed new one. Connected the battery and the car attempts to start without a key in it or turning. Disconnected the battery to stop the car from attempting to start. Any help would be appreciated.

You assembled the ignition switch incorrectly. Take it apart and try again.