When I bought my 2000 S500 last fall, only the passenger front speakers (plus the sub) were working. Since I planned to replace it anyway, I didn't worry about it. Every once in a while, all the speakers will come on and work fine. No static or popping like a loose connection, and no fading in and out. Just a completely normal sound out of all speakers. I used the fader and balance to confirm that all four areas were playing. I moved the amp, and banged on the dash with the heel of my hand to see if I could "break" it, but no luck. Then the next day, back to just the right front. What's up???

 

disconnected/broken wires. have your electrician check the wires

 

On a computer one would say "reboot". Have you tried this option with the Comand system? Both when working and not working? There may be an electonics or software fault in the amp.