you need to wire the line level outputs from the new h/u to the amp. The OEM wiring harness uses a common ground for all 4 channels. Make sure you also connect the remote amp turn on from the new h/u for the amp. If you're uncertain which wire is/belongs to which from the old set up, you can download the owners manual for your old CR-220 directly from
http://www.beckerautosound.com/Porsche/Porsche%20Menu.html Near the back of the manual there is a schematic of the back of the h/u which you can cross ref w/ the wiring harness plugs.
Good luck
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