i know i need the amp and cd changer anything else?

Im assuming its a new car. There's 2 possible problems here:
1. If you are relatively short or just enjoy sitting with your seat far forward you may have noticed that the seat moves back a small distance when you switch off the car/remove the key. This sometimes causes that a small wire under the drivers seat gets caught by the mechanism and gets accidentally pulled out. MB is aware of this problem and if you take the car to any dealer's service department they should change the wire for a longer one for free.
2: If you switch the radio on and it says sound unavailable you have a slightly more serious problem. This often happens when the amp is faulty. On my mother's 2003 s320cdi this is the problem, it does however work if the car has been standing in the sun for a while and the amp has warmed up a bit. Your only option to fix this is apparently buying a whole new amp and having it installed by MB which is a rather costly affair.

Hope you manage to get it working. And by the way, nice car!

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