Starter won’t turn off (Ignition switch Problem?)
 

I’m having problems. My car won’t start, and the starter will continue to run even with the key out of the ignition. Sound like an ignition switch problem?

It could be the switch, or even a bad solenoid that can cause the starter run-on problems. I have had a bad solenoid that would keep the starter cranking with the key removed from the ignition switch. I had to pull the battery connection to make it stop. I removed the wire connections from the solenoid, and found that it was still making a complete circuit, the contacts had welded together. I had to replace the solenoid, no further problems. This was not on my 911, but the starting circuits are pretty much the same. Good luck!! Tony.

sometimes the starter drive gear and the ring gear around the pressure plate that it interfaces with get very chewed up and the starter will hang up as it's cranking. as long as the solenoid is held in the extended position, the starter will keep cranking, even without power to the solenoid from the ign switch.

On my car when I bought it the cold start valve was not connected at the starter the wire was hanging loose under the car. When I hooked it up the starter would keep cranking when I tried to start it. I had to pull the battery connection. But as I live in South Florida I just unplugged it again with no problems since. I do not know what the problem was to make it keep cranking but unplugging the cold start valve was the solution of the previous owner. Cold start valve problem or solenoid problem? I did not try and chase it down but someone else on this sight might have.

While replacing the electrical side of the switch with an eBay version recently, and diagnosing a no-start even with the switch replaced, the switch fell apart when pulling the harness off the back (or trying to). This would certainly be a potential fail point, but I think it's less likely than the other items mentioned.