1982 Cabrio with 16v KR engine won't turn off

Hi all, my car engine wont turn off even if I pull the key out. Its running a 16v engine on carbs. Once I pull the key out, it runs as if the key is still in the ignition. I have to pull the fuel pump relay or disconnect the battery for it to stop. If i stall the car the fuel pump continues to run. Once I reconnect the battery or put the fuel pump relay back it will appear to reset and start up as normal but again wont turn off. I was going to change the ignition switch but something tells me that's not the problem. Any ideas?

Spray some wd40 in the ignition key switch, work it.  See if it is a sticky ignition switch first as that is the highest suspect.