1997 Ford F-150 engine runs after key is turned off

I would start with IGNITION SWITCH 1. To inspect ignition switch for mechanical operation, rotate lock cylinder through all switch positions. Lock cylinder should not bind, and should return from START to RUN position without assistance. 2. If binding or incorrect modes occur, ignition switch should be adjusted. After adjustment, if binding or incorrect modes still exist, lock cylinder should either be disassembled and inspected for damage, or ignition switch should be replaced. 3. To test electrical function of ignition switch, disconnect ignition switch connector. Check continuity between specified switch terminals using a self-powered test light or ohmmeter. See Fig. 2 or Fig. 3 . See IGNITION SWITCH CONTINUITY TABLE. If continuity is not as specified, replace ignition switch.the ignition switch.