If you have the CDR220, this thread helped me to get one installed. If you use the one that connects to the bottom of the ipod and hook up the power lead, you may hear the whine of the hard drive through the stereo. To alleviate this, just pull the fuse to the power lead until the ipod needs to be charged.
http://986forum.com/forums/showthread.php?t=9736&page=1&pp=20&highlight=ipod