What you have is a dash mounted control that has a large din cable, which is routed thru your CD and then to the tuner that sits on the rear wheel housing. There is a fuse on the CD bottom, and a fuse on the tuner. you need to remove the CD anyway to get and the fender liner so you can get to the tuner. The CD gets its power thru a "Y" cable from the tuner, so no eject indicates that there is no power.
E--2
1 check cable from radio to CD
2 check fuse on bottom of CD
3 check fuse on tuner (trunk)
This is from mercedes bulletin and indicates looking for voltages and finally replace.
I think on Beckers web page it shows the install if you look up your car
http://www.beckerautosound.com/1432-1991/troubleshooting_tips.html
go to the bottom of this page it shows it
http://www.beckerautosound.com/1432-1992-93/1432_1992-93%20S-class%20with%20BOSE%20index.html