Thinking that the engine (1985 500 SEL) continuing to run after turning the ignition key switch to "off" was caused by a bad ignition switch, I replaced it with a new switch. However it did not resolve the problem. The only way I can stop the engine is to pull the coil wire. Once I have stopped the engine this way, there is no power to the #15 terminal of the coil. Otherwise the car starts and run fine. The key / ignition switch seems to operate correctly. Everything was working fine until once I turned it off, removed the key, locked the doors, started to walk away and noticed that the engine was still running. What could be going on?? Help!