Engine won't shut off with key

[Dennis]

I read online that run-on can be caused by alternator backfeed and this can be tested by starting the car and pulling the alternator connector. If the alternator is backfeeding, the engine will stop. I tried this and the engine did not stop. The source said that in this case the backfeeding could be in the ignition wire and inserting a diode in that line could fix it. Before I do this I would like to get some other input.

[jiriza84641]

What engine setup do you have?

[RoadRacer]

You didn't mention it, but had you turned off the key before disconnecting the alternator? If not, the battery will keep the car running, without an alternator even being present.

Seems like you have some bad wiring somewhere, you shouldn't have to insert a diode. But I can't help in how to track that down.. but check everything from ignition switch to solenoid.

[NAZ]

How long does the engine run and how do you eventually get it to stop?

If you have an electric radiator fan not wired through a relay, this may allow the engine to run while the fan spools down. Won't run forever, just a short duration. Some fans operate as a generator and depending on how it's wire to the electrical system can feedback power.

[Dennis]

Thanks for all the comments. I didn't mention the engine because I didn't think it mattered. It's an LS 3 376 cid and an AC Delco alternator. I tried pulling the alternator plug both ways, and the result was the same, the engine keeps running. The harness that came with the engine has a wire labeled IGN SW. That wire is spade connected to the orange FFR harness wire labeled, Coil or EFI. The engine stops when these are pulled apart. I bought the engine from Blueprint and they told me to make this wiring connection. I tried putting the IGN SW wire on the terminals of the ignition switch but that did not help.

[michael everson]

Maybe bad ignition switch?
mike