car starts fine but will not shut off when i turn the key off
 

'95 buick century was given to me for doing a job. 118,000 miles one owner. did fine for a week with no problem. so i turn the key off and the eng. will not die. It sounds like it is missing i can turn the key back forward and it starts running fine. After a few times of back and forth with the key it seems like it chokes out and dies.

Not sure if this is the case here, but I believe the condition was called dieseling. This was caused by too high an idle speed and as long as the fuel was available (Carbureted)
the engine kept attempting to run. Some had an idle stop solenoid to prevent this. It dropped the idle speed down when the key was shut off.

Another completely different reason could be a motor was running (like blower motor) and a relay was kept energized by the motor becoming a generator thereby providing power to the ign circuit (Feedback circuit) and the engine kept running. Don't ask me which relay , it's been too long ago. Loved looking for the cause of that type problem.