What is this wire for???

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Marc
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What is this wire for???

Post by Marc » Sun 25 Sep, 2011 6:23 pm

Hi team,

I received my "new old" Becker Mexico last week, so time to upgrade the 90s radio to the 70s radio.

The 90s radio has a nice connector where all the individual wires come together. Before cutting this off, I am trying to work out what each wire does. I think I have the answer for all but one wire. As such, I was hoping someone could tell me what the yellow wire is for.

Here is what I believe the wires are for (from left to right):
Green - Left speaker rear, positive
White/Black - Left speaker, negative
White - Left speaker front, positive
Purple - Right speaker rear, positive
Grey/Black - Right speaker, negative
Grey - Right speaker front, positive
Blue - Electric antenna
Yellow - ???
Red - Power (positive)
Black - Ground (negative)
radio_wiring.jpg
Thanks in advance for your help.

Marc.
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cuisses
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Re: What is this wire for???

Post by cuisses » Sun 25 Sep, 2011 6:48 pm

Marc,

I have done exactly this kind of thing - exchange some horrible aftermarket stereo for Becker in a W108. I cannot remember exactly what the color codes were - but if you are really stuck I can pull my one apart. I also wired it up so I can use the external input from an ipod etc, which is easy to do.

If you look at this video:
http://www.youtube.com/watch?v=5h-VIQMZp24

he suggests red = key on +ve, yellow= continuous +ve. (i.e. yellow is always on even when the car is switched off).I have wired my Becker up so it works even without the key.

This code seems reasonably common (google "car radio wiring color codes"), but not universal, so it might be best if somebody else confirmed this before you fry your Becker :angry4: .
David Williams

W108 280SE 4.5 (Papyrus White and Palomino)

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Greg in Oz
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Re: What is this wire for???

Post by Greg in Oz » Sun 25 Sep, 2011 7:20 pm

As David mentions, it is usual for head units to have both a permanent +12V supply as well as a switched +12V supply (via ignition switch position 1), at least for head units manufactured over the past 25 years or so.

If the mystery wire isn't to allow for both permanent and switched power, the other one missing from your list is +12V for dial/display illumination. Many head units allow for power via the lighting switch so that the dial/display illuminates with the instrument lights, or in the case of some modern units with LCD displays, to allow the display to be lit brightly during the day and more dimly at night when the lights are in use.
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Marc
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Re: What is this wire for???

Post by Marc » Sun 25 Sep, 2011 8:24 pm

Thanks for all the quick replies.

In case of my Becker Mexico, I can see where all the wires have to go. Based on David's comments, I would say that I need to use the red wire for power; i.e. radio comes on when the key is in the ignition. There doesn't seem to be an additional input on the back of the head unit, so perhaps there is no need for the yellow wire.

Greg, I'm not sure if the lights in this radio have the ability to dim in the evening. David, does your Becker dim it's lights in the evening/when your head lights are turned on?

Marc.
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Re: What is this wire for???

Post by cuisses » Sun 25 Sep, 2011 9:27 pm

David, does your Becker dim it's lights in the evening/when your head lights are turned on?
No, it is always bright. The way I have wired it there is no way for the radio to know what the lights are doing. My radio is a Becker Grand Prix i.e. no cassette player and a separate amplifier and automatic station searching. I also have a separate Mercedes fader with the proper Mercedes knob , which I fitted into the dash on the right of the steering wheel, as there was already a hole there which was being used for a defunct car alarm light. All in all, with the separate amplifier, and fader, and ipod connection to the centre console and front and rear speakers there are wires all over the place. The amplifier is supposed to go behind the glove box, whereas all the leads to the speakers come out at the centre of the dash. My son saw all these wires and asked "Dad, how do you know which wire goes where?", to which I replied "Because I am a physicist." - I like to think my degrees are not purely academic, although I am not sure you have to go to university for years just to wire-up a radio. The wiring is in principle straightforward, but there is an awful lot of it.
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Re: What is this wire for???

Post by Ivanerrol » Sun 25 Sep, 2011 9:28 pm

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Re: What is this wire for???

Post by 4heckssake » Mon 26 Sep, 2011 8:35 am

I think it is usually that the yellow is for constant power and red is powered with the ignition on (could be the other way around??). If your Becker is a grand prix or one of the models that stores radio stations in its memory you will need the constant power in order to 'save' the memory. otherwise you will need to search for the station every time etc.
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Re: What is this wire for???

Post by Marc » Mon 26 Sep, 2011 9:02 pm

Ok, I decided to get the multi-meter out and work out what is what.

First I measured straight on the battery: 12.44V
Then I measured the red wire: 0.09V - 0.44V
Next, I measured the yellow wire: 0.09V - 0.44V
I then measured the red and yellow wire with the key in the ignition (position 2): 0.09V - 0.44V

I noticed that the red and yellow wires have some fuses further up the line. I checked those and they were fine. I even measured before the fuse on both wires with the key in the ignition, but I am getting the same results.

Any ideas?

Marc.
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Re: What is this wire for???

Post by cuisses » Mon 26 Sep, 2011 10:32 pm

Does/did the old radio work?
What are you using for ground, i.e. what i the -ve terminal of the meter connected to?
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Marc
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Re: What is this wire for???

Post by Marc » Wed 28 Sep, 2011 9:06 am

David, you're a genius. Thanks to your last comment I used a different ground point and everything worked the way expected: yellow is "always on" and red is "on with key in ignition". I cannot workout why the ground point used by the previous radio (which was working normally) is no longer working. I spent all of yesterday evening getting everything ready and it works!

Just have a bit of noise on the rear speaker, but I can troubleshoot that later; perhaps a ground loop or a wire that I didn't connect properly.

Thanks again!

Marc.
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Re: What is this wire for???

Post by Marc » Thu 29 Sep, 2011 10:10 am

Hi team,

I was troubleshooting the noise issue a bit further. First of all, it is only there when I turn the volume up considerably. I swapped the cables for the left and right channels and found that the noise travels with the speaker, indicating that the wiring is OK and that the issue could be in the external amplifier.

I will need to take the amp out, open it up and see if there is anything obvious inside. Does anyone have any ideas what I should be looking for?

For now, everything is fine for iPod use: I keep the volume on the Becker low and use the iPod's amplifier to get decent volume.

I would be keen to hear people's ideas on how to troubleshoot this issue.

I read through this article: http://www.termpro.com/articles/noise.html
Very useful! But didn't resolve my issue.

Marc.
280SE 3.5 - 1972 (Sofia)
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Re: What is this wire for???

Post by cuisses » Thu 29 Sep, 2011 10:51 pm

I am assuming your radio (like my own) has an amplifier separate from the actual tuner.
What I would do first is isolate if the fault is in the tuner or the actual amplifier. When you put the ipod signal into the tuner it will be pre-amplified in the tuner bit before going into the amplifier (it is this pre-amp which allows you to control the volume via the tuner knob). The fault could be with the tuner pre-amp.

Take the amplifier proper out of the car and hook it up to your home stereo and see if it misbehaves. If it doesn't then the fault is in the pre-amp. (You can run the tuner signal through you home stereo to confirm this).

If the amplifier proper is misbehaving you could look for dry joints in the soldering, but in my view you really have 2 options:
(a) Take it to an expert to fix.
(b) Just replace it with a modern amplifier. These are likely to be cheap and better than the Becker, and since it is hidden nobody will ever know.

If the tuner part is at fault I think I would just take it to an expert.
David Williams

W108 280SE 4.5 (Papyrus White and Palomino)

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Re: What is this wire for???

Post by timelord9 » Wed 19 Oct, 2011 11:39 pm

Most of the time noise like that is due to a bad earth. If you suspect the amp, I would check and re-re check the amp earth wire and chassis earth point. Also check the connection between tuner and amp.

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Re: What is this wire for???

Post by Marc » Wed 11 Apr, 2012 11:35 am

I was just browsing through some old posts and came across this one. Between a couple of months ago when I was installing the radio and now, I have found a work-around for the "noise in the rear speaker" issue.

My Becker-Mexico comes with a hard-wired cable for AUX input (i.e. an iPod). This cable ends in a female earphone jack. The idea is to plug in a male earphone cable and plug the other end into your iPod. I always left the cable plugged into the female earphone jack. If I remove that cable when I want to listen to the radio (or a cassette :happy3: ), the "noise in the rear speaker" problem is gone.

Bottom line: only use the cable when you want to listen to your iPod.
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Re: What is this wire for???

Post by AMG » Wed 11 Apr, 2012 8:21 pm

low frequency oscillation or 'hum'

occasional high frequency which increases with engine rpm or 'motorboating'

usually indicates a ground loop somewhere.

the tip of your 1/8 stereo phone plug is the left channel signal. if it is touching something which provides a complete circuit to the ring or the base of the plug you are creating a loop between the unamplified input and the earth or chassis ground. the result will be a broad hum at a pretty much constant set of frequencies.

always unplug the connection from the amp or you risk damaging your precious speakers - not to mention the possibility of blowing up a circuit on your amp.
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