Detecting when the ignition is off in my car?

[JDMils]

I have an Audi A4 B7 2005. With the OEM head unit, the unit would stay on when the ignition was turned off and would go off when the key was removed.

I have replaced the OEM head unit with a Kenwood after-market unit but the installers could only get it to stay on when the ignition is on- once the engine is turned off, the head unit goes off. i would like the head unit to stay on until the key is removed, just like the OEM unit but the installer says this information is only available via the CANBUS system in the car- so the OEM unit instead of sensing voltage levels, was being sent codes from the car's computer to tell it what was happening with the ignition switch.

Is there any way I can "decode" the CANBUS system to create a circuit board which can convert the codes back to voltage levels which the after-market head unit can work with?

I do not know what the codes are nor what the wiring diagram is. Thanks.

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[smoka 10+ year member]

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check them out to see if they have a canbus adapter for your vehicle