1990 300SEL W126,

My becker died again after get it refurbed only 2 years ago. I decided to just replace it with an aftermarket head unit. I would rather not go through the trouble of bypassing the amps If I can avoid it. I followed the advice in this thread:

http://http://www.peachparts.com/shopforum/car-audio-multimedia/276276-w126-headunit-replacement-keeping-factory-amps.html

Where it says how to use the low level output wires and connect them to rca cables to use the factory amps.

I believe that I have to connect up the white and yellow wires to the RCA plug ground from the stereo and I also ganged it with the shielding ground (brown wire) but I have lost all of my bass.

Funny thing is if I disconnect the brown, yellow and white wires I still get sound but it is really tinny and then when I reconnect them the sound improves but it is still lacking base. Im confused. I guess I don't really understand how the brown shielding wire fits into the puzzle.