1995 Ford F-150 truck won't shut off, ignition problem

Truck stays in on mode, replaced ignition and it was not that, took steering colum apart and there is a white square thing that goes up and doen when you turn your key on and off and it goes all the way down to start the truck and then you try to shut it off and the top part comes back but the bottom part stays in run position. Not sure if this should be one piece and it is broke or if it is suppose to be two. No one seems to know what I'm talking about at the automotive stores and even went to the Ford Dealer and another mechanic. I can manually push the bottom part up with a screw driver and it will turn off but don't even know what this part is to fix it. Can someone help or advise. 3F723 is the part # I got off a print from dealership, and the part that is broke (?) Is in this part. Do I need to replace this whole part and has anyone ever done this. It looks hard to change a lot of stuff has to come apart?