It's been ~30 years since I last replaced a car stereo myself. Last time was easy, it was a basic American make car - ~1970s vintage, and all the wires matched up on the old unit and the new unit.

Now I'm replacing the stereo in my 83 300d.

I'm doing this on the cheap, cheap, cheap. My new radio is a Dual system from Walmart. The Dual has a wiring harness and diagram in the install instructions, with the following wires:

1 - Blue (remote turn on) for power antenna or amp. (I replaced the power antenna with a non-powered antenna, and so I will not use this wire.)

2- Black = Ground

3- Red = Accessory (from ignition)

4 -Yellow = memory (direct hot to the battery)

The 4 wires that go into the plug (the numbers below are on the plug) for the Becker unit are:

1 Brown
2 Black
3 Gray
4 Red

Can someone tell me what these wires are coded for? I have the battery out of the car so I can't test for ground, hot, etc. I don't know if it's safe to assume black=ground or if Mercedes or Becker used some other wiring code in 1983.

Second, the speaker wires. The new unit has 8 wires for speakers, hot and ground for RF, LF, RR, LR. The becker unit had 2 plugs for speaker wire, each plug having 2 wires into it. The car ('83 300d) has 4 speakers and a fader switch in the center console, does this mean that the speakers are mono and I only have front and back, but no "right" or "left" in the current wiring? If so, would I just combine the right/left wire pairs from the Dual to wire up the front with both RL wires to the hot and both RL wires to the ground, ditto for the rear, and then end up with mono sound?

I am not an audiophile. I just want to get radio without sporadic static (current problem), and have a USB plug for my iPad. I can live with mono. The diesel is really noisy, stereo or better speakers probably won't make much difference considering how noisy it is in the car. I'm just trying to get this new stereo installed with the current speakers for now, and then I'll explore putting in better speakers if I'm unhappy with the results.

Voila:

Becker Car Radio Stereo Audio Wiring Diagram Autoradio connector wire installation schematic schema esquema de conexiones Anschlusskammern konektor

The numbers are reversed, but this will get you what you need.

On the car:

Brown = ground
Black = switched +12
Gray = dimmer switch (cap this off or you'll blow your cluster/instrument lights since it's apparently not used in your new radio)
Red = unswitched +12.

You should verify with a meter between the black and the red which is switched and unswitched. Some radios have a thick red (typically switched) and a thin red (unswitched). Wire colors are not a sure bet due to variations.

The OE speakers are Left and Right (I think they have L and R on the plugs, or possibly green is right, red - left).

The easiest way is simply to connect a basic "stereo" setup using either the front or rear ONLY from your new unit. You may/may not have problems with the fader and power from the HU since the impedance on the speakers may be off from the allowable range. That'll route the sound through the old fader. Since that spot in the console is prone to spillage, you may also still get static.

My advice would be to fish the wires out from BEHIND the fader and unplug the rear speakers from the harness. Or you can pull the fader harness slightly forward and cut into the wires to isolate the negative channel to each speaker. When you unplug, you're sure; when you cut, you're not sure until you test.

I put in pics and a diagram here: w123: Speaker Wiring Myths Debunked (Diagram) Bypassing the fader

Read the whole post since there's mis-information in the early parts.

Note the last post or two referred to static until they separated all four corners.

Assuming you're using the cigarette lighter as power, keep in mind that the ashtray is part of the circuit and it needs to be opened fully to engage the clip. You may want to pop that out and clean the connections to prevent unneeded heat build up due to poor connections.

Thank you, this is exactly what I needed!

Stupid speaker wire question. I have 2 pairs that are red/black and green/black (that were then each wired to a red/green pair and plugged into the Becker unit, but I went up the wires past a junction to unearth their original colors).

Per the above, red is left. But, is the red wire the + or - wire in the pair?

In the OE speaker pairs of wires color is +, black is -.

It sounds like you now have two each red/black + black (left F and R) and two each grn/black + black (right F & R). Have you unplugged from the fader and tested each pair with a 9 v and listened for static? It's an easy check to make sure which pair is which and that you're ready to connect to the HU.

UPDATED!
For the Becker Grand Prix Electronic 612 on my 85 300D, the pin assignments are as follows:

The link below and the picture of my connector show:
1. Ground - Brown
2. Switched 12V - Black
3. Illumination - White (or Grey?)
4. Permanent 12V - Red
(see pic below)

I am about to install an Alpine CDE-100. It has the following connections:
6. Ground - Black
5. Permanent 12V - Yellow
4. Switched 12V - Red

Interestingly, it has a tag on the yellow wire that says 15A Battery and it is heavier than the Red, which is labelled Accessory. The yellow is also a heavier gauge than the red.

From above, it would seem my connections will need to be:

Car-->Radio plug
1-->6 Brown to Black (Ground)
2-->4 Black to Red (Switched 12V)
4-->5 Red to Yellow (Permanent 12V)
3---- White/Grey Capped

Becker plug pin-out: harness
Alpine manual: http://support.alpine-usa.com/products/documents/OM_CDE_100.pdf

Comments welcomed!

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

The wires are the same, but the pin numbering is reversed in the two links. A white wire for switched +12 sounds odd, but the colors are not always consistent. I try to verify with a meter whenever possible. If the wires are still in the OE fitting, you're safer than if the PO hacked them.

Your connections look correct.

I don't think the permanent +12 uses a 15A fuse, but I wouldn't upgrade from what's currently in there unless it blows with radio use. Fuses 1, 2 and 4 all go to the radio in some fashion, including the illumination.

The wire gauge is also reversed I think. The permanent +12v used to be for the clock, so it was skinny; while the switched +12v was for the music, so it was fat. New HUs reverse this by having a skinny switched wire and a fat permanent wire. The OE wiring should be adequate, but you might want to consider a separate power line and connection if you're going to use the cig lighter to run an iPod or something, too.

You can also connect your power antenna: blue from the new HU to the Bu/Rd or Bk wire in the car that went to the antenna pin on the old radio. That one can be traced pretty easily to the antenna switch, if you're concerned. It'll be dead until connected to the HU, so that's a tougher one to ID.

Funny those wire colours are reversed. But my car was original. Still have the plug so will double check. And with meter too! (ADDED: I did and I had two of the colours reversed - corrected in post above)

Re antenna - Mine has been bent one too many times, so I have it disconnected. I do have a new antenna, so maybe I will at least connect the wire at the radio end, so if I ever get around to it, the antenna will retract. I should be able to find it because it should still have a plug on end.

Thanks for comments!

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

If it's only the mast that was bent and the motor's still functional, they're pretty cheap (maybe $10-15 usd). Just double-check to verify the toothed or smooth style nylon cord. There are DIYs on that, too.

YAK & Others

Please note that my post about pin assignments on my 85 300D had an error - I have corrected it and added a picture of the connector.

I realized my error when using a meter to double check voltages on the wires.

Thanks Yak for alerting me to this!

BTW - The Alpine CDE-100 is installed. I chose it because it had the most reserved looks befitting an old Benz But it has some neat features for a low end radio - ipod socket on front, but also a USB port. Apparently I can insert a memory stick loaded with MP3s.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Looks like a clean install.

Is that a M-B temp gauge in the center? I've seen 126 (I think) digital readouts added to the dead space in the bottom center of the cluster, but that looks different.

Not a bad look... what is that gauge above the HVAC control?

Scale on the guage goes from -## to +##.

I'll bet that it's a amp meter.

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2013 Volkswagen Jetta Hybrid SEL Premium (Sparky)
http://badges.fuelly.com/images/smallsig-us/193500.png

It's a car not a science experiment! Open the throttle!

OK - Three questions about the mystery "gauge"

Actually it is just a magnetic thermometer! My brother used to own a MB dealership and gave me few of those along with some star keyrings many years ago. Still have a few of them.

BTW - It's on crooked - being magnetic it goes where it wants

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Very cool! Never seen one of those before.