w123: Speaker Wiring Myths Debunked (Diagram) Bypassing the fader
 

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

If it helps. . .
 

The harness that came with my stereo was a GM connector. I found it's car side mate pretty easily. It's only 12 - pin and it's got everything I need.

Metra 70-1677-1
Metra 71-1677-1

http://www.installer.com/wires/

Clarification
 

Thos,
Your post is inspiring! However, could you please elaborate on "Cutting the spliced grounds"? MY car is an '87 and I'm not sure of the extent at which my stereo differs from yours. I have 8 wires snipped from the fader (you had 6) which I have pulled through the cave, and the 4 wires (imposters) which came from the radio output. Are you saying that if I stip the sheath from the fader bundle, some spliced wires (grounded) will be found and I should use them for the negative lines of the front speakers? Or are these to be simply unspliced?
Thank you and for more information on my situation, please see my post here in Car Audio forum.

Freybird

That's what I found. The two grounds from the Front and the two grounds from the Rear speakers are spliced together up inside the sheath. A third pair of grounds is spliced in there also to ground all four speakers to two channels of the stock radio. (see diagram)

But. . .this is the w123. Do you have six speakers stock instead of four?

For me it was really helpful to have found a junked car with zero interior that let me trace everything easily.

I did see and read your post, but the 8 wires at the fader throw me.

One thing I did notice is that ALL of the grounds on my car were solid black whether they were front or rear.

Whatever you do, cut that sheath off, just so you have all of the wires free to work with. I imagine you'll discover something similar.

Good luck. Maybe post some pics of your set up too. If I can I'll add pics down the road from some other w123.

T

Wow. This actually worked. My '85 300D-T was slightly different as far as wiring (I discovered two sets of soldered grounds when I opened up the sheath), but the process was similar. Very useful post.

Joe

Thanks for this post

I just was confronted with this same problem and was looking for a solution

Nice Admin...:),,

Does this wiring diagram hold true for the 300 SDL as well?

Also, are the colors shown on your diagram accurate?

I just tried this and If u have the fader intact, you can just use the wires into the radio. Cut the connectors there split the 2 wires the black connector is the left side, the white is right. You will have 4 wires, 1 each for + and - for left and right coming from the dash now. Splice the + & - together from your deck (e.g. rear right and front right) and connect the corresponding side to the wires coming out the dash. What you should have when u are done are a pair of wires from the deck to each wire in the dash. this will give you fader control in the center still.

An old trick used in car audio biz is to connect a 1.5 volt AA battery and touch to the speaker leads temporarily to hear the click in the speaker and that will tell you which speaker goes to which wire.....

And polarity too, so you watch the cone move out or in when the + and - poles of the battery are touched to the wires.;)

Your post mostly reflects confusion.

Of course each speaker has two wires. That's how speakers work.

However, the OE rear speaker wires BEGIN at the fader, i.e. there is nothing near the radio.

The old radios are 2-channel, meaning there are only +/- connectors on the radio for left and one pair for right.

Therefore the left/right pairs extend from the radio directly to the fader. Then two pairs (four total) extend from the fader to the front and rear speakers respectively.

All new radios are 4-channel, meaning there are 4 sets of connectors at the radio. Left/right for front and left/right for rear.

"Common ground" is completely irrelevant as both the OE radio and any new radio features +/- pairs of connectors for every channel.

The wires from the existing rear speakers have to be, at minimum, EXTENDED to reach the radio. (Because they BEGIN at the fader, which is separate from the radio) On a W124, at least, they have to be cut from the fader to accomplish this--I bet it's the same on a W123.

There aren't any myths, there's just your confusion.

Which sheath contains the missing grounds? I just snipped my fader connection and snaked the 6 wire sheath back up behind the radio. I can't really see where the 4 wires coming from the radio meet up with the 6 from the fader though. The wires back there are pretty tight so I can't move them around too much to check.

The 6 wire sheath you snaked back up to radio area contains the grounds.

After I snaked this sheath to the radio area I had to cut the wires due to their over length. But, your wiring might have been modified previously.

Hey Thos, great post! This is exactly what I was looking for!

Quick question, when I cut the sheath that was holding the 6 wires, I found three (!!) black ground wires connected together. Does anyone have any idea as to what I should do?

Thanks for the help! I really appreciate it. I took some pictures that I can upload on the center console removal process if anyone has any questions.

Just separate all the grounds... if you fish the wiring out of the center console you can see that all the speakers have a + and - wire running to them... if you get it all fished out you will see what I mean... you should have two red wires and two green wires and then there will be four black wires total...

This is all assuming you have four speakers in the car already....

(This is how my '83 300D was... I just did it on Friday so it's still kind of fresh in my mind :D )

Hey Cap, I had 1 red, 1 green, 1 red/black, 1 green/black, two blacks (these were all connected to the fader in the center console), and three black 'soldered' together (that were in the same bundle of cables, just hidden further in the sheath).

In addition to that, I had the original 4 cables that were connected to the radio but from what I've read, these are the 'imposter' cables.

Does it matter which ground I use for each speaker (i.e. doing the battery test to see which speaker blips)?

Thanks for the help! I am new to all of this so I am learning on the fly.

Good job with the battery... if the speaker "blips" then you have the correct + and - for that speaker. The speaker shouldn't make any noise if you dont have the right ground.

You might not have traced the wires far enough back if you don't have "8" wires. Basically you should have four "colored" wires and four black wires... you need to cut the grounds apart that are connected together. Follow the wires towards the radio opening. IIRC There are a set of the connectors like the ones that plugged into the back of the radio where the rear speakers connect to the wires that plug into the fader switch. you can get rid of the connectors and now you will probably see what I'm talking about.

If you still aren't quite sure take a picture and post it of the wires you're talking about. You shouldn't need any extra wire for the speakers. Just one wire for constant power. You can splice into the emergency flasher wire that has constant power and just run a short wire (maybe 2') up to the radio and then you will be golden. I found this idea on the forum so I wont take credit but it's a good place to splice because you don't have to run a long wire up into the dash.

-David

Hey Cap,

So I went a little further back and I found some more ground cables... so now I have 11 cables!! (that were in the sheath)

I have:
1 green
1 red
2 red/black
2 green/black
5 black


I attached some photos. Also, to what does the gray/purple illumination wire attach to? Thanks again!

http://farm5.static.flickr.com/4142/...71ef66efce.jpg
http://farm5.static.flickr.com/4122/...f88f7fcfa7.jpg

http://farm5.static.flickr.com/4077/...96ff27aa87.jpg

(see more here: http://www.flickr.com/photos/37518110@N03/sets/72157624403069354/)

This isn't quite true, at least not in the W123 coupe and probably sedans.

Yes, there are 6 wires at the fader. And yes, there are 4 wires at the factory radio head; but two of those wires are different ends of the same wire (Rd/Bk = L; Gn/Bk = R).

If you want to eliminate all guesswork, remove the factory fader harness and UNPLUG (yes, that's correct - unplug) the rear speakers from the fader harness. You may need to remove the center console, but you know for sure where your wires are.

If you're determined to cut, then on my factory '83 300CD harness, the solid green wire = RR, solid red = LR; the black/combo wires in this sleeve both are FROM the radio and TO the front speakers; green = right, red = left.

There are SIX black wires, not four. Two from the radio to the two separate solder junctions and four from the speakers. The solder joints are about 15-18 inches away from the factory radio plugs.

There's nothing magic about the wiring, and the 123 did have a "common ground" for each side. That's what the blob of solder is.

I am installing a new unit on w201 but it is the same problem as the w123.

Instead of cutting the wires at the fader, can't you just 'tap' onto the wires you wish to have leads to?

the fader is going to act as a resistor within this design and should not cause any problems - fader bypassed.

*this is a question as much as it is a statement.

If the W201 and the W123 have the same fader harness, then they share a ground, so if you want to isolate each corner, no, you can't just tap into the wires.

If you don't want to cut any wires but don't want to run new wires to the rear speakers, I think there are a few options: you can unplug the rear speakers from the fader harness and run new wires to the front speakers.

Or you could possibly unplug the fader switch, disconnect the rear speakers from the harness and pull those wires forward to the head unit (possibly enough slack), and then use the taps on the respective sets of now isolated front and rear speaker wires.

Either way, you have to unplug everything and/or cut something. I unplugged it and ran new wires to the front only and re-used the rear wires in my '83 300CD.

I am keeping the stock radio but my fader is shot. Can I just wire nut the three wires on each side of the fader together and have equal speaker feeds on all four corners?

btw I have a subwoofer and a factory amp in the trunk.

The speakers are in parallel at the fader. I called Becker Service department and asked if I wire nutted the three wires on one side and the three wires on the other side together would I just have full power to all four speakers and he said "yes". I took my console apart, pulled the fader and blew it and the plug out. It works perfectly now. I believe this is a good first step when diagnosing the Becker system.

Do you have the speaker wiring gif in higher resolution for the speakers?

Try right-clicking and open in new window. The lines are legible then.

But since this thread has a fair amount of confusion and mis-information, maybe starting a new one with a specific request and/or problem might be more useful.

Or you can look here for the FSM page for the W123 radio wiring: post 54

http://www.peachparts.com/shopforum/car-audio-multimedia/284681-240d-frying-radio-fuses-4.html?highlight=fader

something to chew on
 

I put a new headunit in yesterday, opting to use this thread and the old wiring for the rear speakers.

I re-wired the front speakers because it was easy. The rears, however, are obviously a little more complicated.

I was checking out the sheath feeling for the spliced in grounds. Beneath that bundle I spotted two pairs (green/black and black, red/black and black) of wires that look exactly like the speaker wires that plug into the original headunit. I found these under the console, in the front-right corner, right under the sheath that carries wires to the fader. I was confused why these speaker wires weren't in the sheath with the others.

Additionally, right in this spot the wires were split by a connector, identical to the plugs at the headunit (one flat prong, one round prong, on a round plug). This connector is also found south of the rear speakers. I unplugged the two sides, and tested the prongs with a 9-volt. They made the rear left and right pop, respectively. I pulled the rear speakers to check the color coding, and found that my rears (84 coupe) are wired with red/black, green,black striped wires and black grounds, not solid red and green as the guide here says.

I'm curious why these wires are here, in front of the fader, if they ran to the rear speakers. They did not appear to just feed into the fader, or the sheath. They are four separate wires from the six at the fader. Just in case I tested the connections at the fader with the 9-volt to see if I could make the rear speakers pop, but got nothing with any combination.

I went ahead and used running wire splices to tap into the +/- of the wires that i found, and ran new wiring from here to the new headunit. Viola, seems to work great.

Post #20, above: "If you want to eliminate all guesswork, remove the factory fader harness and UNPLUG (yes, that's correct - unplug) the rear speakers from the fader harness. You may need to remove the center console, but you know for sure where your wires are."

The rear wiring on the coupes (and others, maybe) plugs into the fader harness, but is long enough to be snaked all the way to the front.

The guide may refer to the colors inside the sheath, i.e. between the fader and the rear-plugs and not the colors of the wires from the plugs to the speakers. I used to have a picture of the removed fader harness, but can't find it. The harness is with the new owner.

I agree that on the coupes anyway, tracing back and unplugging from the soldered/split/multi-wire harness is the cleanest way to go.

I read post #20. I agree the cleanest way may be to snake the bundled wires back through the cave. Doing this and clipping/dismantling the fader harness, however, is not the best way to keep things intact so you can re-install the factory radio if you need to.

No body has mentioned the wires i'm talking about, and tapping into them seems like a pretty good way to avoid dismantling the fader as well as spare you from re-wiring the rear speakers. My concern is that i'm still unwittingly passing through the fader. The fader harness is unplugged, so I don't think this is possible. Has anyone tried testing the rear speakers with a battery at the fader harness?

I don't like this thread due to the incorrect info sprinkled throughout. I've drawn a schematic and included a labelled photo of what I'll call the fader harness. It starts at the radio with 4 wires, the two black (-) wires are spliced with four more black wires at the two solder blobs. So you've now got one black "input" per blob and two black "outputs" per blob or four total black "outputs". Each of these black outputs goes to a corner connector (white = left, black = right, they're also marked R and L).

The colored wires from the radio go directly to the fader. That's one red (or red/black) and one green (or green/black). At the fader, there's a rheostat and four outputs two each red (or R/BK) and green (or G/BK). The fader basically splits the one red (or green) input into two each outputs. These four outputs go to one each corner red to the left and green to the right. These four colored wires join up with the black wires from the above paragraph.

The front speaker connectors are actually soldered (the long way around) to the black wire at the HU radio connectors, and the front colored wires are connected at the fader.

If you run new wires for the fronts (pretty easy in the W123) and simply unplug the rears DOWNSTREAM of the fader, then the fader harness stays intact. You don't need to run new wires to the rear.

The numbering code between the drawings is:

ONE: four wires at the head unit, red + bk; grn + bk (red and green and red/bk, grn/bk are used interchangeably in the drawing since I didn't have a stripe tool). The black wires from here go to---
TWO: two solder blobs in the sheath. The colored wires go to---
THREE: the fader, where they split again and go to four plugs at ---
FOUR: four speaker connectors, two in the console and two near the speakers in the dash where the wires rejoin their black counterparts last seen dividing at the solder blobs.

great diagram, Yak. BTW, I got signal to all four speakers OK without separating the commons, just tapped into the ones on the 4 wire set that was originally at the head (but still used the 4 coloreds coming out of the fader). Does that affect my sound i.e. do I need to go back in there and separate the four? I've got some static in the system I'm trying to run down, wondering if that has anything to do with it.

If I understand what you've described, you've bypassed the fader by re-using four of the six wires there (the four that go to the speakers + terminals, but you're still using a common ground for the the front and rear channels. That might be causing static, but it's tough to say. You could maybe do a quick diagnosis for static by unplugging one set or speakers and seeing if the static clears up. Is it static, like crackly, or a whine/hum? If the latter, that's probably alternator noise.

The other problem about tying the speakers together has to do with the impedance of the speakers and the power output of the HU. If they're not compatible, then you can burn out the amp in the HU. This is probably not a problem if you're not cranking it up.

Thanks. Yeah, I dug down and separated the wires. No static now (other than when i turn it up loud - but that's because of the old speakers). My back right isn't working, although it gives me a crackle with the battery test. When I'm rich enough to replace my speakers I'll worry about that.

Just rearranged the speaker wiring on my 85 300D.

It was arranged as Yak described. In other words, positive wire from each speaker goes to fader. Also, the positive wires from the back of the radio go to the fader.

The negative wires from the speakers terminate about 1ft short of the fader under a plastic sheath. The negatives from the back of the radio terminate at the same point and are soldered to the left or right hand speaker wires making two 3-way joints. Yaks drawing shows this.

What I did, was:
- cut off the fader plug
- pull off the sheath on the fader harness after removing a couple of tie-wraps under console cover. (this exposes the soldered negative joints)
- taped over the soldered joints, then used the smaller sheathed wire that connects to the radio, to pull the wires into the radio opening.
- I then snipped off the solder joints. This leaves the speakers wires in pairs - the long one (colored) is the positive and the short one (plain) is the negative
- It is easy to see which wires are which for the front speakers (see below for my colours)
- For rear speakers use flashlight battery to make speakers click to find out which is which.
- Hook everything up and Bobs yer Uncle :)
(see http://www.peachparts.com/shopforum/2926132-post6.html for power connections)

For my 85 300D:
Front left speaker - Green/Brown
Front right speaker - Red/Brown
Rear left speaker - Yellow/Black
Rear right speaker - Black/White

The speaker wire colours on this wiring diagram don't seem correct

1985 300D that had Becker Grand Prix 612, now with Alpine CDE-100.

I just want to take the time to tell The Don that I love him for this thread.

Middle of the night, leaving on a trip next morning, installing a working radio, this thread solved all my problems

Thanks Thos, When I saw only 2 speaker connections on the back of my old Becker it stopped me right in my tracks. With all the helpful info on this thread I was able to continue on with my audio upgrade install. I completed it successfully. I replaced my front speakers with drop-in 3.5s from Crutchfield. The stereo was part of a $90 set from Pioneer (Walmart online) that came with 2 6x9s and 2 6.5s. I put the 6x9 in the rear. I now have much improved car audio. I had planed to put the 6.5s in the doors but, I don't think I need to. Thanks to all who posted on this thread.

Thanks,

thanks so much just started on my [new for me] 1993 300D 2.6 Turbo, bad Mercedes radio or something I assume so I have an old DUAL i will put in cut the fader wires Now I will hope to hook up 4 speakers, got to be better than my phone and or old ambulance with 2 speakers, jaaa

Wiring Stereo W123
 

Thanks for the thread


Here’s what worked for my son and me on our 79 300TD.
Cut all wires at existing stereo and at fader.
Non-speaker wires coming from the engine side were:
Yellow (constant battery +)
Red (fused, switched +)
Black (neg)
A quick voltage test from the yellow and red to the black confirmed this.

Then we pulled up the rear speaker wires from under the cover behind the shifter – they are easily identifiable by the little clip-on joints (a black one and a white one).
Cut them off too
Stripped off all wire ends.
Now we had a number of mystery wire ends to identify

Did a continuity test to see which ones paired up, and made a list of them.
On each pair, did the click test with a 1.5v battery to see which ones lead up to a speaker.
To check polarity, we undid the cover of one of the front speakers and noticed that connecting +ve to its solid color wire made the speaker diaphragm rise, and connecting –ve made it fall, so we identified the solid color as +ve. We then assumed that all the other solid colors were the positive and used that as a rule of thumb. (This ended up working perfectly but see note below about the black ground wires).
Soon we identified each pair of speaker wires, and were left with four wires that seemed to serve no purpose. More testing showed that they simply went from the radio to the fader. So we have left them tucked inside.
We used the conventional codes for our stereo found easily on the web and soldered up all the 8 speaker wires, solid colours for + and striped for -.
Now interestingly the black grounds that were soldered to the rear speakers were all soldered to solid colour wires. This contradicted our findings about the polarity of the front speaker. Nevertheless we wired everything consistently and the sound we now have is perfect