Help with aftermarket cd player in a 87 mercedes 260e?

i am putting my older benz back on the road and had to replace battery and other things. The last time i drove the car i noticed my aftermarket eclipse deck was having some problems reading the disc i would get errors but sometimes it would play. I always noticed i could not hear anything from the rear and the the speakers i did hear were very faint. well after getting the car from my mechanic we installed a new battery and i noticed that i could not even hear the radio this time. the car sat for over a year from the last time i drove it. i dont think its the esn from the eclipse deck cause its not asking me for the code. i also noticed after a while i was hearing static but it just was static not like anyone talking on the radio or music playing. i did notice that the antenna on the mercedes was not going all the way up nor down but i had pulled it all the way up but didnt hear anything. i really do not want to go through the trouble of rewiring the car. i plan on putting a older panasonic ghost head unit to replace the eclipse. is it a good possibility that my deck is garbage or maybe fuses? i really dont under stand why i never heard anything from the reas from the day i bought the car and how terrible the front speakers were. if it is not a hard i would not mind upgrading the front speakers and maybe throwing in some 6'9 in the rear. does anyone have any experience or maybe have a clue on what might be my problem? hoping it something small. Also do you think its going to be hard switch out head units? i do have the wire harness for both but i have a feeling it being german im going to run into problems with color coding. also i read online that maybe when the first wired the aftermarket head unit in that they might have ran wires to the battery maybe my mechanic disconnected those and could be causing the problem?