I just replaced my cylinder key lock set because the key did not go in all the way and it didn't go all the way back to the off position. I replaced it thinking it would fix the problem. We installed it properly and it seemed fine it turned on and looked good but when we tried removing the key again it didn't go to the off position so I couldn't remove the key , then I disconnected the battery and I tried then and it let me take out the key so I know the cylinder is not faulty , what can it be?

When you move the gear shift to park (on an automatic car), a switch is depressed that allows the key to be removed from the ignition. Either the car is not in park, or the switch needs to be replaced.