Why factory deck need to stay in car?

Hi Guys,
My factory deck display burnt out and it started smoking. I removed the deck and opted to buy an after market deck. At the store they told me my deck needed to stay in the car even if I installed a new one using a long wiring harness to keep factory deck in the trunk.

Why?

at the electronics store they said car wouldn't work without it. Thats a lie, I took deck out as soon as it started smoking.
At my local dealer ship they couldn't explain why. At the 1-800 number for oldsmobile they also couldn't help me.

Does anybody know why the factory deck needs to stay in the car?? And can I install an after market deck without needing my smoking deck in the trunk? It'll probably be locked anyway.

Any help would be much appreciated.

O ya thanks Xeroinfinity
It's a 2001 olds Alero

Welcome to AF.

It would be nice to know the year and make/model.....

But from what youve stated you probly hav a newer Olds.
So, the deck only has to be in for the chimes to work and maybe some other minor things.
An aftermarket stereo will work, though your anouying chimes wont work.

I thought some aftermarket company sold a wire harness for the fix but I'm not certain where to find it.

Thanks Alot!
If all I'm missing out on is the door chimes I think I can live without that :)