Greetings!

I have a bit of a problem and thought I'd see if someone here could help. When I shut off the engine by turning the ignition key to the zero position and even taking the key out, the motor is still running and I have to use the manual shut off switch. This is something to new to me and I'd appreciate any help for the experts here.

My Mercedes is a '82 300TD Station Wagon. Thank you and happy holidays to all.