my123 sorry to say it looks like lock replacment is on the books for you .Had this with one of my cars .It was an Humber Snipe .I was the culprit .The key was stiff going in ,so i put a little grease on the key, i pushed it in a few times .Started it up would not stop after i turned the key off. The contacts in yours have worn out in the switch .. Look in the tech info top of this page .All repairs under the sun in there check it out .