It is unlikely that an in-dash radio would have a 200W peak or RMS output without a Power Amp. If there is one then you probably need to wire up the Power amp separately with a hefty fused 12V, directly from the battery.
I do not understand why the installer reused the fader by the shifter. The fader circuit in old MBZ is NOT a true Front/Rear 4 speakers setup. One must run separate wires to the rear speaker, or cut the wire at the fader to by-pass it completely to have true F/R speakers. If your new radio has F/R channels then the fader need to be by-passed. Speaker wires should be easy to sort out but make sure the phase is correct. Some radio or power amp also has subwoofer set up, so there could be a lot of speaker wires. Control wires are all the same.
Audio equipment - radio, power amp, subwoofer, speakers, tweeters and monster cable could easily worth more than the old MBZ.
