i have some diagrams for the becker system on a 91 560sel. let me know if this would help. i can send it to you. basically, the head units feeds into an amp installed inside the trunk. The then feeds into the front and rear speakers via the fader wheel. The front consists of front door speakers and dash speakers. For the rear, there are 2 amps installed behind the backseat that powers the rear speakers( one for each channel).