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Old 3rd Aug 2018, 3:11 am   #1
Novusuhu
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Default Vintage 70's 'Realistic' car radio wiring

Hey everyone

Yesterday I found a vintage car radio from 'Realistic' (Radio Shack) with casette player.
I'm sure it's from the 70's (I think 1976.)

I have a problem with the wiring. I did some research on the internet, and I think I got most of the wires right...

Here is what I got:
Green - Left speaker
Grey - Right speaker
Red - +12V
Black - -12V
And the Antenna connector ofcourse.

But then there is one last black wire from which I don't know what its function is...

Do you guys know what the function is?

Here are some pictures:
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Old 3rd Aug 2018, 9:11 am   #2
paulsherwin
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Default Re: Vintage 70's 'Realistic' car radio wiring

At a guess, it controls an electric telescopic antenna. The antenna would retract when the radio was switched off.
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Old 3rd Aug 2018, 11:28 am   #3
'LIVEWIRE?'
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Default Re: Vintage 70's 'Realistic' car radio wiring

What is printed on the label attached to that black wire? It seems odd to use black for a wire which will be at +12vDC when the radio is switched on, but a quick check with a multimeter set to a low ohms range will establish the wire's function. If it is common with the red wire with the radio switched on, then it is indeed a switched +12v supply line for an Automatic or electronic aerial, or maybe the trigger (switching) line for an external Booster amplifier. This check should be carried out without power applied to the stereo. Alternatively it can be done with a +12v supply connected, but without anything connected to the black wire, by using a meter set to DC volts ( a 25 or 30V F.S.D. range is best in this case. Either an analogue or digital meter can be used for these ckecks.
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Old 3rd Aug 2018, 12:55 pm   #4
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Default Re: Vintage 70's 'Realistic' car radio wiring

Again, strange for it being black, but another possibility is it is connected to the lights circuit of the car so that the radio dial is illuminated when the parking or headlights are turned on.
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Old 3rd Aug 2018, 1:27 pm   #5
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Default Re: Vintage 70's 'Realistic' car radio wiring

Didn't think about that one, Terry, but whatever is printed on the label attached to the Black Lead should make clear its purpose.
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Old 3rd Aug 2018, 5:20 pm   #6
crackle
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Default Re: Vintage 70's 'Realistic' car radio wiring

What about speaker negative, sometimes these were individual as they needed to be separate for each speaker.
Have you tried the Radio Museum, it has a wiring diagram for a Realistic car radio cassette, not quite the same as yours but the wiring may be the same. https://www.radiomuseum.org/r/radio_...c_12_9257.html
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Old 3rd Aug 2018, 9:16 pm   #7
julie_m
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Default Re: Vintage 70's 'Realistic' car radio wiring

You should be able to see what it is connected to using a multimeter. Select a low ohms (Ω) range, and measure between the mystery black wire and each of the power leads, with the set switched off and on in case the switch is in circuit, and with the probes both ways around in case there are any diodes in the path. Post all 8 results, together with the readings when the probes are not connected to anything at all (open circuit) and also with the probes touching each other (short circuit).

It most probably will be either another earth connection, or a supply to an electric self-extending and retracting aerial which is only connected when the radio is on. (Do all the above tests without a cassette in the slot, in case inserting a cassette cuts the aerial supply -- after all, there's no need for it to be deployed when listening to a cassette, and some people would be extra impressed by it retracting under such circumstances. Otherwise, what's the point of even having an electric aerial?)

In any case, the measurements won't lie .....
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Old 3rd Aug 2018, 9:55 pm   #8
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Default Re: Vintage 70's 'Realistic' car radio wiring

Quote:
Originally Posted by 'LIVEWIRE?' View Post
Didn't think about that one, Terry, but whatever is printed on the label attached to the Black Lead should make clear its purpose.
I labeled the wires myself...
The label on the black wire is still blank. Because I don't know its function yet.
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Old 4th Aug 2018, 2:08 am   #9
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Default Re: Vintage 70's 'Realistic' car radio wiring

Is there a model number printed/stamped on it anywhere?

If there is nothing on the outside, carefully unscrew and lift the lid off, the information was sometimes pasted inside the lid on Realistic gear.
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