As dumb as it sounds when i first bought my stang i couldnt figure out how to turn the key back far enough to get it out , little did i know there is a button under the steering colum! lol. As far as your problem goes i have no clue , fords have wierd things like that , my bronco will run without the keys , and i can take the keys in and out of the ignition at all times.
Ok i got it fixed, (and my car doesnt have the button you have to push), i had to take the plastic cover off the steering console, and i had to spray some wd40 where the key turns, Now it turns just fine....sorry to bug ya..
The actual ignition switch (not the key part) is notorius for failing after a while on these cars. I've had two in my 87 coupe so far...
Same symptoms.
I had a similar problem a few years back on an 88 GT. I couldn't get the ignition switch to turn at all when the key was inserted. I ended up calling a locksmith, and he used some tool that looked like a mini knitting needle to fish out a piece of metal that had somehow gotten in there. We thought it might have been a piece of the "key-in" sensor, but nothing was adversely affected afterwards (except my wallet)