having a problem locating the cd changer....i have searched the trunk and found nothing.....in a 2000 s500

 

it should be under the floor mat next to the spare tire !
or on the left side of the trunk

 

Guessing your car does not have one installed, believe they were optional.

 

left side trunk in the enclosed compartment. if it isnt there some one took it, i dont think you could spec an s500 without it. if they removed it than simply play single discs in the nav drive until you can get the factory unit replaced.