Myth 1: The w123 uses only one set of wires going to the front and back set of speakers, instead of the standard two.

Myth 2: To use all four channels of a newer head unit = must run all new speaker wires.


Yes, there are only two sets at the radio, but. . .
it is not necessary to run all new wire.

You do have a +/- for each speaker. It's true. Stay with me.

I just finished putting in a Sony head unit and 10 disc changer into my '82 240D. After much head scratching, alot of searching to glean from other folks' experience and a trip to the junk yard, I made it happen; My first stereo install.

The w123 is not a common ground system (which, I've read, is bad juju). Each speaker has both +/-. What's tricky is the fader and what's been done to tap two stock channels to drive four speakers.

As for the fader, I knew I had to bypass it (apparently it can't handle the power output of new stereos) so I just opened up the console, pulled the switch and snipped.

I snaked those six wires back up past the shifter and pulled them out through the radio cave(DIN opening).

(Keep in mind that the original harness plugs had been disappeared long ago (thankfully).)

Curiously, I now had 10 (ten!) spkr wires to contend with; 6 from the fader and 4 that were hooked to the radio outputs.
The 6 are your friends. The 4 are imposters and have hidden the grounds that you need in the sheath that ran to the fader.

Have a look at the diagram below - cut open the sheath that you worked so hard to snake back up and find the spliced ground wires.

You should soon have 8 wires (4+ and 4-). The fronts are still paired. For the the rear spkrs, find which ground is which by using a 9v battery (the speaker will crackle when you've got a match).

Good Luck. I know it's a long post but I hope it helps someone out.

I couldn't have done it without this forum. T

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'82 240D, 215,000 +
Classic White, Regenbogen