mbz 1992 300e amp bypass

I am looking to install new sony head unit in 1992 MBZ 300E. Ordered unit form Crutchfield and was told I was told I would have to rewire all the speakers directly form new head unit because of ground problem. I this correct ? I thought I remembered doing one of these before and that you could just go to output side of amp in trunk area to connect speakers or possibly connect at fader near center console. Any input on installation in this vehicle would be helpful. The existing system is stock Becker radio / cassette, system 1432 I believe.

If you have a thumbwheel fader in the console I don't believe there is an amp. See if there are male/female speaker "T" connectors behind the deck. If there are, separate them. One set should go to the front speakers while the other should go to the rears via the fader.There is no such thing as free installation!

Thanks for the response, this vehicle does indeed have amp in right rear trunk area as I just looked at it. Amps and tuner are all located here. Anyone have any idea how and where to bypass these.

If it's a high level input you can just connect amp input output leads. If not, you need to run wires to the trunk.There is no such thing as free installation!

Thanks again, what I really trying to do is get specific information on color codes and location of speaker leads so I can bypass factory system. 

No one has ever worked on this car?

Usually I just figure out the wiring as I go, with a speaker popper...Too many vehicles to keep track of.