To reset the service light on a Mercedes-Benz M Class, disconnect the positive cable on the battery for a few minutes. If this does not do the trick, turn the key on and pump the gas three times then turn the key off. Start the vehicle. The light should be off.
The cd changer in the 1998 Mercedes Benz E320 would be located in the trunk of the car. If you are not able to locate the cd changer in the car or trunk, it may not have been included. The cd changer may have been an optional feature.