lock and cylinder will not return to lock position it only goes to start positio

Start or 'on/run' position? Is it in park....completely? 12.5 volts or better at battery?Steering wheel move free?

I'm pretty sure that year had a cable that runs from the key switsh to the parking pawl. this is a safty feature to be sure the car is in park, before you can remove the key or start. Check to be sure it is not broken or come loose. Newer cars now use the brake switch or electronic lock for the same purpose.