The 1st detent should be lock, and the only place you can remove the key.
The 2nd should be off.
The 3rd should be run.
The 4th should be start.
The ACC location on the switch is usually only accessible by turning the switch counterclockwise from the lock position.

If you want to listen to the radio and not have the ign turned on, why not run the radio directly to a fused battery plug? You will have to turn the radio off when you don't want it to play, or it will be on all the time. Gene