Hate to say it, but sounds to me like the cable/switch is kaput. You mentioned that it was hard to operate for a while before it got stuck - whatever broke in there took its time until now.

I don't think the trouble is with the cable-ignition interlock. That thing makes it so you cannot turn the key to "off" while the cable is in the run position (keeps steering from locking up while driving). I can pull the cable in mine with or without the key in the ignition switch.

I think you need to pull the instrument cluster and have a look. Maybe the trouble is something simple after all, and it might be lurking back there.