For stereo reinstall, do I need unit serial # or VIN too?

[zippinbye]

Getting my 1995 960 ready for sale. Before I remove the aftermarket stereo, I need to know the prospects for my success in getting the Volvo stereo to operate. Mind you I have the original AM/FM cassette unit, but the car came to me with a AM/FM CD unit, I believe out of a later model 850 (assumption based on the box of parts and manuals that came in the trunk). I'd prefer to run the CD unit, since it's more useful and I know for sure that it's fully functional.

If I understand correctly, I need a code to reactivate due to security measures? I'm uncertain of that, because I have detached the battery for days and the stereo still worked. I'm not sure how unplugging it and removing from the dash is any different than de-powering the whole car, as far as the stereo knows. Internal memory battery or angle-sensing mercury switch? In any event, I need to know if just the stereo serial # is sufficient to obtain a code. I have no idea what car it came from in regard to VIN #.

Thanks for any assistance you can offer.

[difflock54]

The VIN number is needed to identify the specific vehicle and its original radio unit. The security code is unique to that original factory installed radio unit.
If the radio you have now originally came from another vehicle, then your cars VIN is not going to help determine the replacement radio head units security code number.
Take a note of the currently installed head unit's full serial number as they may be possibly able to track down its security code directly despite the VIN reference now being irrelevant.
Sometimes the 4 digit number has been written on the casing of the head unit especially if it was salvaged for resale.