Dear Car Talk:

I have a 1969 Buick with a 430-cubicinch engine.

It will start and run fine. But when I go to turn the car off, it keeps on running, even though the key is all the way in the “off” position. The only way to stop the engine is by disconnecting the positive cable of the battery and turning the key to the crank position.

The only thing to add is that when I go to put the positive cable back on, it sparks like something is on, even though nothing is on.

Any help would be appreciated. -- Bob

OK, how about if I help you write a classified ad for this thing, Bob?

Actually, I think the problem is your ignition switch. The ignition switch is on the side of the steering column.

The ignition switch has three or four positions. There’s the spring-loaded “start” or “crank” position, which temporarily fires up the starter motor until the engine is running. There’s the “run” position, which is where the key springs back to once you release it. In the “run” position, power goes to the coil, which powers the spark plugs.

There’s often an “auxiliary” position, which lets you run a few low-powered accessories. My wife uses that to listen to the radio while she waits for me outside the butt-lift clinic. And then there’s the “off” position, in which there’s no power going to anything. Except on your Buick, Bob.

I think your switch just wore out after a mere 55 years. It’s allowing electricity to power the coil even in the “off” position. And once running, engines will keep running, unless something interrupts them, like lack of fuel or lack of spark.

That’s also why you see sparks when you reattach the battery terminal. It seems like something is on because something IS on. The switch is, effectively, still in the “run” position.

So, ask your mechanic if he can test the ignition switch for you. My memory of ‘69 Buicks is thankfully fading, but I think you may be able to unplug the switch without taking the whole steering column apart. That would allow your mechanic to plug in a new switch and try it out and see if it solves the problem.

If it does, then he can remove the steering wheel, pull the column apart and permanently install the new one. Then your car will “not run,” like most other ‘69 Buicks.