I have a 1989 Plymouth Grand Voyager, 3.0L , automatic transmission, with a tilt steering wheel. I drove somewhere and parked. When I tried to turn off the car, the key would not move from the Run position. I tried tapping the key lightly with a hammer but still the key wouldn't move. I tried moving the key to the off position with the transmission in every position , P thru 1, but the key didn't move. When I tried to remove the key while it is in the run position, the key came out maybe 1/16". The key is a copy of the original, but I've used it for maybe a year. I finally stopped the car at home by plugging the air intake. I later discovered I can move the key to the start (crank) position and start the car.

How can I fix the problem?

 

Going to need a new switch; something has come apart in there.

 

I had the same problem with an 89 Cherokee. Turns out the return spring broke, so I had to put in a new switch. To turn that off, I disconnected the battery and it wouldn't start again until the new switch was installed.