My car has fiber optic cables for a CD changer and telephone. My problem is that once the CD changer is installed using the factory installed fiber optic cables, it does not work (HU displays msg: "no CDC"). I've done a flashlight test on the fiber optic cables, and there is connectivity from head unit to the CD changer. Also, assuming a cable might be mislabeled at the factory, I have arranged the fiber optic cables using every possible combination--still no success. I have concluded there must be something other than cable connections that is required. But what is it?