I have nothing to complain my old Becker radio. It works perfectly. Every single function works. But it won't play my CDs, mps's... 

It is said that it is very difficult to swap a CD player into the mercedes 10-speaker sound system. Because Mercedes used two separate Amplifiers behind the back seats, used a separate Fader under the center console, and their speakers are 2-Ohm rated... unless you change them all ---- speakers, amplifiers, wires and bypass the Fader.  Yes, I saw people do this, and the new system will be fantastic! But it also costs a lot, and it would take a pro to do the job right for 3 days.

There are many owners out there they do not want spend too much, they want keep their W126's original stuff as much as possible, they want do the right job for a quick. I figured a solution and I did the job right in my 560SEL.

I have kept every component of the Mercedes sound system, except the head unit -- a must, or what's the point, right? I did not cut any existing wire harness. The sound quality is better than the original Becker radio simply due to a newer head unit which uses the lastest audio technology developed over 16 years since the production of the old Becker radio.

I did my job in two phases. In phase I,  I home made two 3-pin plugs. I hooked the CD player's line outputs to the Fader, so did the power lines and ground line. It worked! But I needed to turn the volume control to MAX to get good sound. Some CDs did not pop enough volume still. This was due to the fact that the new CD player's line output signals did not 100% match the Mercedes amplifiers' input signal reqirement. In phase II,  I took off the coupling amplifier from the back of the old Becker radio, and I used this coupling thing to receive CD players line outputs and then feed the signals to the fader just like what the old Becker radio did. At this stage, my job was completely accomplished. Now I can enjoy my CDs, MP3s, and many more...