What's this plug behind the radio???

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francoid

What's this plug behind the radio???

Post by francoid »

I can't identify what this is, or what to do with it as I rewire a new harness for my new radio on the 1985 635. Every other wire in the original harness that was behind the radio is properly identified and tagged, this is loose... Thank you for any pointer!

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hornhospital
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Re: What's this plug behind the radio???

Post by hornhospital »

I have the same stray wire behind the radio in my 633. Same color plug, same color wires. No clue what it's for. I couldn't find it in the ETM.
Ken Kanne
'84 633CSi "Sylvia"; '85 635CSi "Katja";'85 325e "Hazel Ann"; '95 M3 "Ashlyn"
francoid

Re: What's this plug behind the radio???

Post by francoid »

Interesting... Is your radio setup OEM or has it been modified?

There's a function I am missing as I connect the new radio. It's "illumination", i.e. letting the radio know when the headlights are on and it needs to go into "night" illumination mode. Does that function exist on the OEM radio? If so, could it be the stranded wire?
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Re: What's this plug behind the radio???

Post by hornhospital »

Mine is an OEM radio (I don't know what model). It does not have an automatic dimming function when the lights come on.
Last edited by hornhospital on Sat Sep 10, 2016 3:33 am, edited 1 time in total.
Ken Kanne
'84 633CSi "Sylvia"; '85 635CSi "Katja";'85 325e "Hazel Ann"; '95 M3 "Ashlyn"
francoid

Re: What's this plug behind the radio???

Post by francoid »

Darn (but thanks).
Do you know whether the ashtray light comes on at night only, or all the time?
I'll try and do some testing tomorrow regardless but wondering...
Thanks
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86_6series
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Re: What's this plug behind the radio???

Post by 86_6series »

Ash tray lights with light switch.
86-635CSi
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francoid

Re: What's this plug behind the radio???

Post by francoid »

That might be an option. Hope I don't fry my radio...
Does anybody know whether illumination is straight +12 v?
Thank you!
francoid

Re: What's this plug behind the radio???

Post by francoid »

Ok, this is interesting. The ashtray lamp indeed is based upon the light switch. However, the voltage I find there is 6v, not 12v. Now I have to figure out whether that's appropriate for my "illumination" pin. Argh, why are things never simple?
francoid

Re: What's this plug behind the radio???

Post by francoid »

Well well. The voltage between the two wires that lead to the bulb is 6v, however on second check, the wires are +12v and +6v as referenced from the ground, therefore I can use them. I have checked ISO norm 10487 and confirmed +12v on the wire will mean reduced ambient light / night visibility conditions. The expectation is no meaningful current drawn, I am not going to insert a relay there. I think I'll just splice from the +12v lead on the bulb and cross my fingers.

With that, I have all the leads I need. I have already spliced the ISO B plug (speaker level output) to 2 pac-audio SNI-35 line adapters (one for front and one for rear) to which I connected RCA cables to the amp in the trunk. The ISO A plug is simpler (only 5 live wires: switched +12v, antenna remote, illumination, battery direct +12v, ground) and I'll complete it in the morning.

Funny how simple projects take a life of their own...
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Re: What's this plug behind the radio???

Post by baders »

The cigar ash tray light is part of the dimmer circuitry. Therefore, you will have variable voltage according to what position the dimmer is set.
1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
francoid

Re: What's this plug behind the radio???

Post by francoid »

baders wrote:The cigar ash tray light is part of the dimmer circuitry. Therefore, you will have variable voltage according to what position the dimmer is set.
Now you really got me. Got a couple questions please.

What's the "dimmer" you refer to? Is it the potentiometer that goes with the low beam pull on the dashboard, where you can adjust how bright your dash is?

And how does that work for the ashtray light? I see +12v and +6v, would that go to +12v and 0v if brighter? If so, all good for me. I am ok with a binary mode on the radio, I think that's all it will take. On the other hand, would not help me if the +12v lead fluctuated...

I would test but have pulled the battery cables to splice in power cables.

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Re: What's this plug behind the radio???

Post by baders »

francoid wrote:
baders wrote:The cigar ash tray light is part of the dimmer circuitry. Therefore, you will have variable voltage according to what position the dimmer is set.
What's the "dimmer" you refer to? Is it the potentiometer that goes with the low beam pull on the dashboard, where you can adjust how bright your dash is?
Yes. It is part of the light switch and operates by rotating the knob. The ash tray light is part of that circuitry. The potentiometer is actually in the ground leg of many instrument/dash lights.
And how does that work for the ashtray light? I see +12v and +6v, would that go to +12v and 0v if brighter? If so, all good for me. I am ok with a binary mode on the radio, I think that's all it will take. On the other hand, would not help me if the +12v lead fluctuated...
It is all about voltage drop. Picture the light globe and dimmer pot in series and the light switch set to the park position. If the pot is set to maximum (brightness), there is 0v voltage drop across the pot. In this case there will be the full 12v voltage drop across the globe = full brightness. If the dimmer pot is set to minimum (brightness), there will be a voltage drop across the pot. I don't know the value of the pot, but say it is 6v drop. There can only ever be 12v across the entire circuit, therefore leaving in this case 6v across the globe = minimum brightness.

I don't know what sort of signal your radio would need but I suspect it would be a discrete signal, not a variable one. You need to hook the battery up and test.
1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
francoid

Re: What's this plug behind the radio???

Post by francoid »

Makes sense. I believe I am good with taking the positive lead as source for illumination. I have checked that it shows 0 when lights are off and +12v when they are on. That'll give me a binary signal, unlike the analog one controlled by the potentiometer, but upon reading the ISO standard it does not appear the standard expects analog, continuously varying input.
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