13.8v dc cb radio wiring

Discussion in 'General Electronics Chat' started by zachiswhat, Mar 15, 2012.

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  1. zachiswhat

    Thread Starter New Member

    Mar 15, 2012
    I have an older cb radio which I am installing in my car. It runs on a dc connection but the power cord has been lost with time. ive gotten a replacement for it but its universal so the tab on the radio that makes sure the plug is in the right way on the back is useless. On the new power cable I know which side is positive and which is negative BUT on the radio itself which side would be positive and which would be negative?
    I've included a picture. So if anybody could help is the Left or Right pin positive? Please forgive me if this seems like a dumb question as I am clueless :)http://tinypic.com/r/10ojqs2/5
  2. Wendy


    Mar 24, 2008
    A valid concern, I hate it when manufacturers do this. Can you get a manual? It may take some searching, but it is possible you can get it online.
  3. zachiswhat

    Thread Starter New Member

    Mar 15, 2012
    I have googled the crap out of this thing but it was manufactured by such a small company there is really nothing listed for it. I even went as far to tear it apart and see what color the wires were on the inside but of course theres nothing to distinguish them.
  4. Pencil

    Senior Member

    Dec 8, 2009
    Post a picture of the inside. Maybe someone can help if
    they see the inside.
  5. K7GUH


    Jan 28, 2011
    I assume by now you have opened it up to see what's inside. If you can identify any part of the circuit that looks like "ground", it's a pretty good bet that it's the negative. Using even a cheap multimeter, test from the part that looks like "ground" to each of the two wires for power. The one which gives a zero ohms reading, or close to it, is the "ground". The other one should be more than zero ohms to "ground", but not necessarily a lot more.
    Now, if you are adventurous, apply 12 volts positive to the not-negative lead and battery negative to the negative lead. It's a crap shoot, but the odds are in your favor that the unit won't instantly die of reversed power leads. If you are less adventurous, put a two amp fuse in the positive lead before hooking it up. If it blows, either you have reversed leads or the unit draws more than two amps on receive. While you have it open, take pictures from every possible angle and post them here. There may be enough info there for us to help you out.
  6. neurovangelist

    New Member

    Mar 13, 2012
    Hello Zach. If you have a VOM meter, try probing both pins, with one of the probes going to the chassis (or case) of the radio. If you have infinity on one of the pins, that should be your ground. But be sure to check both of the pins to make sure. Or probably the best way, if the radio has a fuse, probe the pins to the fuse, and if you get infinity on either pin that will be the positive. Worth a try. Post the info of the radio here that you have, and I will see if I can find the manual on it. Or e-mail me n5pjy (at) hotmail dot com.
  7. zachiswhat

    Thread Starter New Member

    Mar 15, 2012
    I would like to thank everyone for their ideas, after much probing around I decided to just take a guess and go for it. I mean I had a 50/50 chance on it and it is such an older radio I didn't care if I blew it up but luckily my guess was right. Its now hard wired into my car and working beautifully.:)

    thanks again,
  8. Brownout

    Well-Known Member

    Jan 10, 2012
    Next time, use a diode bridge, just as you would use to convert AC to DC. No matter which way you plug your device in, the voltage will be correct. Once you use the bridge to determine the correct way, then remove it from the system. You're voltage with the bridge will only be about 12.3V.
  9. BSomer


    Dec 28, 2011

    umm... I point out that this is incorrect. You should get close to zero ohms, which means that there is a connection. Infinity or some other high value of resistance is no connection or a connection through a lot of components.
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