Adding a CD Changer
 

My 2003 996 C4S came with the M680 option, the Bose MOST radio/amp, but not the front-trunk-mounted CDC-4 CD Changer. Is adding that changer a simple plug-play operation (i.e., is the wiring harness for it already in place behind the trunk linings)?

I had a similar setup in my 2000 Boxster

If my memory serves me correct when I added my CDC4 in the front trunk I needed to buy the CD cable and the CDC4 unit.

There was no pre-existing wiring for me and I ran the cable through the front bulkhead in front of the speedometer cluster area to the front trunk and attach the cd unit on the other side of the amplifier unit

Take a look at the amp in the trunk. The connections should be on the right side (passengers) of the amp.