Hello and welcome to Just Answer.
Does it run smoothly or a little rough?
It runs smoothly.
Has it had any modifications to the ignition system or wiring?
Does it have the original ignition system in it or has it been modified. Many cars of this age have had their ignition systems upgraded?
We just installed a new ignition switch when the car would not shut off when the key was in the off position. The new ignition switch worked correctly for two days and then it went back to not shutting off again. That is all that has been done to the ignition system.
I worked on these when they were new.
I am very familiar with the ignition systems. I cannot come up with any reason other than another faulty switch for this to be happening.
Thats why I asked if there had been any other modifications.
If you unplug the switch when the car is running does it stop?
We took the plastic cowl off so we could unplug the switch like you suggested.
My husband started the car one more time before he was going to unplug the switch. When he turned the ignition switch off, the car turned off like it should and it has worked corectly since then. Thank you for your ideas on working through this problem. Where is the ACCEPT button so I can pay you?
I am pleased its working - you might find the switch isn't returning internally when you turn the key back.