07 Yukon Denali runs without key in ignition

[Amddenali]

My Denali has been at shop on and off for 3 months. Intermittent problem where vehicle is shut off and key is removed but still runs. Local Firestone dealer replace ignition control module, ignition switch, key, cylinder but still does it. It was happening when damp outside but does it randomly now. Going to take to dealer this week. The Firestone dealer, local dealership that was consulted is stumped, and many professional groups say it's impossible based on the diagnostic steps that the vehicle should be still running. Only 100k miles on this truck. Any help would be appreciated. Thanks

[Duelin]

Has there ever been any after market electronic accessories installed in this vehicle?

[Amddenali]

None. Odd thing is everything will be fine, shut vehicle off, come back out and before key is inserted the check engine light is on. Technically no power should be on.

[Amddenali]

About 1 year earlier did have a power brake assist hooked up for the trailer.

[Duelin]

The next time that it continues to run without the key. I would pull the Crank/Run relay. If it quits running I would start my diagnosis from there. It might just be the relay is bad. But that has to be determined. Also If pulling the relay didn't effect it I would trace back where that brake controller was tapped into. If it got connected into a Data Line system you don't know what kind of problems it created.

[Amddenali]

Thank you.