A fiber optic cable may be a little thick and usually has a clear prong on the end, almost certainly capped to protect the glass inside it. The other parts of the wire would be the power to the changer and the control cable from the fact stereo to the changer unit. I have no idea where the cable is located in the S-Class, but I will say that fiber optics will give you unparalelled sound quality. They transmit totally digitally, and receieve no interference from anything whatsoever. I use them on the stereo at home.

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2002 Mercedes-Benz E320 4Matic
1995 Mercedes-Benz E320 Wagon
2005 Land Rover LR3 V8 SE
1999 Audi A8 4.2L quattro