Cannot turn ignition switch backwards to lock steering wheel.

1991 Crown vic. Cannot turn ignition switch backwards to lock steering wheel. Has anyone had this problem? What is the fix for this?

What do you mean exactly?? Does the ignition switch actually turn off, so that you can remove the key??

Look for problems with the trans. selector. If it doesn't go all the way into Park, the lock cylinder won't turn all the way to the locked position.

The trans selector has no problems. You can put it in park and all the other selections. The engine can be shut off. The lock cylinder will not go past the off position in order to actuate the lock. I tried a different
lock cylinder, but still have the same problem.