1999 Discovery II engine not turning off. With the ignition switch all the way to the left, dashboard lights are on, and radio and air are off. Once car is turned on, turning the ignition switch all the way left does not turn off the car, but radio and air conditioning turn off. I have to pull the spark plug fuse or ignition relay under the dashboard to turn the car off.
Here is a video:

This started a few weeks ago, when the car would not start one night. I would hear a single click and then nothing when turning the key. Lights and everything came on like full battery so that was not the issue. Came back to where it was parked the next morning, and it started on the first try. I turned it off and it would not start again. Tried jumping the starter to make sure that it was still working and it spun freely. I was about ready to give up when it decided to start again. Drove home, and the car would not turn off. Pulled the spark plug fuse to turn it off. Started turning on directly from the ignition switch without a problem, so the not starting might have been the ignition switch coming loose, as it basically fell out when I took the bottom steering wheel cover off.

So far, I have replaced the ignition switch and swapped all the engine bay relays around with no change to the issue. Have also tried waiting a few minutes for the engine to turn off, and it does not. It still drives fine.

 

In the fusebox in drivers compartment, there is an ignition relay, square/yellow, believe it is the left lower one. It may be sticking, especially, if water or moisture have been introduced, leaky windshield.

 

Swapped those two around, with no change.

 

Did you replace entire ignition switch, tumbler and electrical/switch portion? I'd go back to the ignition switch area, since you had a known issue there. Maybe the tumbler portion of the ignition switch isn't turning the switch properly?