So my new to me 90 350SDL has only the left side (both front and back working), but no right on the Becker original. Balance adjust does not help.

Was this a weak link (sorry if this was discussed a zillion times) in the W126's or could just a wire/socket be loose, corroded or fallen off?

Should I be looking for a rebuilt unit vs. and older working unit (that will break due to it being "weak")vs. a "new fangled" replacement?

Thanks,

PK

Under the upright rear seatback there is an amp and wire coming from the trunk area. Where those wires plug into the amp there will be corroison, most likely. Unplug the wire plug from that right amp and see if you can clean both the wire plug end and the plug on the amp. How do I know...? I spent 3 months part time and accidently found out what was wrong.

Thanks for the tip. Would I access from the trunk or pull the seat? I'm going outside to look and see if I can see from the trunk side. Any additional info/help is apperciated.

PK

I am very sure you have to access the amp & connection by taking out the rear seatbench and then the upright seat back. You should see the amp & wires plugged into the right amp on the wall behind the seatback. I am reasonally sure you cannot get there from the trunk.

Now understand the dash radio is just a faceplate type unit . The real guts to the radio is the tuner on the passenger rear fender in the trunk. It is behind a cardboard panel. That tuner has connections that goes to both right & left side amplifiers. It also has a fuse but that is OK if the drivers side speakers work.

Chances are that tuner unit is OK. Few people have had the troubleshooting experience I have had. The fader switch between the seats could be the trouble but if that seems to work OK and is not staticy when rotating the switch, all is most likely OK.

Also know that Amps rarely if ever go bad but the wire plugs get corroded which is how I found my problem. Be careful not to bend those prongs in there. I used sand paper and white vinegar and anything that would fit in the small opening to scratch the corrosion off those prongs. Dont put the back seat in for several days until you are sure the problem has been cured. Good Luck.