Glenn: I'd have to research a little on what the 99 C-class had available, but yess, what you've found is the pre-wiring for the phone. I didn't think a 99 C-class had a bumper antenna, but if you follow the lead and it passes through the body in the area of the bumper, then that's what it is alright. The smaller coax I believe goes to the center console, it is the antenna wire that is used for the handset for the "portable" style phone, I believe a 99 used a Motorola Startac. The electrical connector with the data-cable style connector would connect to a "Y" cable that connected to telephone equipment, either a PSE for a portable phone or a TRU in the case of a mobile phone (if it was available in 99). Is there a fiber optic connection on the left? I know there is one on the right for the CD changer. I'm not 100% sure, but I don't think much of this would be of use. The 3 wire connector on the right side might be. I don't know if it will mess up the factory radio by trying to use these 3 wires or not. I would think you would be able to use the power and ground as a trigger signal to turn on the aftermarket equipment, but you may need to have a dealer reprogram the radio to show an installed cd changer, even though it is not there. It may work OK as is, though. I'm still curious, as I can't remember, this does have a "normal" power antenna, right?
Gilly