This link and the DIY article (under DIY tab at the top of the page) are good starting points. It will show how to bypass the fader, which was only designed for 2 channels of power output.

http://www.peachparts.com/shopforum/showthread.php?threadid=18778&highlight=fader

__________________
John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

Click to see 87 300E