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Old 06-28-2010, 09:19 PM   #1
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DC power cord question


Hey everyone, I have a noobie question for ya. I have a dc power cord that plugs into a cigarette lighter that I am going to use to run my cb radio in my vehicle. I cut the end off and have the 2 wires exposed. My question is how do I find out out which wire to connect to my hot and which one to connect to my ground. One wire is black and the other wire is white. Thanks for the help!

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Old 06-28-2010, 09:22 PM   #2
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DC power cord question


Use a continuity tester or multimeter on the plug you cut off to find out which wire was connected to which contact. The contact on the tip of the plug is positive, and the contact on the side is ground.

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Old 06-28-2010, 09:28 PM   #3
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Is there any other way to find out besides using a tester?
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Old 06-28-2010, 09:33 PM   #4
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I suppose you could take the plug apart and see which wire's connected to what contact. Otherwise, you could guess that the black is probably ground, and white is probably positive. 50/50 chance, with the price of a new CB radio as a wager...
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Old 06-28-2010, 09:41 PM   #5
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I took the plug apart and it looks like the white wire attaches to the fuse. So I assume that would mean that the white wire is positive?
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Old 06-28-2010, 09:50 PM   #6
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That should almost definitely be the case. If the fuse holder unscrews from the tip of the plug like a lot of them, then definitely.
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Old 06-28-2010, 09:57 PM   #7
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Yea the white wire leads to a piece of metal that touches the fuse. The black wire hooks onto a piece below the white wire, so Im almost positive that the white wire is positive.
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Old 06-28-2010, 10:04 PM   #8
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DC power cord question


Connect the wire you think is positive to the positive of the radio. Connect the negative of the radio to the metal frame of the vehicle. If you have the positive correct the radio will come on. If you have the negative of the plug connected then radio then radio will not come on as you will have it connected to negatives. Should not damage the radio.
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Old 06-28-2010, 10:27 PM   #9
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How would I connect it to the radio? Sorry Im a noob when it comes to electrical know how.
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Old 06-29-2010, 09:04 AM   #10
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Quote:
Originally Posted by Wims2205 View Post
I took the plug apart and it looks like the white wire attaches to the fuse. So I assume that would mean that the white wire is positive?
10-4 good buddy
What is on the back of the CB for connection points? Are there wires hanging out the back or is there some kind of plug?
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Old 06-29-2010, 12:44 PM   #11
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Should not damage the radio.
Only if the manuf. paid the extra ten cents for a diode inside the radio, or a fuse. Otherwise, the radio is creamed.

Another way to find polarity is to borrow a lamp from one of your taillights and run it to the battery positive terminal. If the lamp comes on when the other lamp terminal is connected to wire X, wire X is connected to the negative batt. terminal.

The cig lighter is fused, probably at 10A. How much does your radio pull?

Last edited by Yoyizit; 06-29-2010 at 12:59 PM.
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Old 06-29-2010, 01:54 PM   #12
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You should know on the radio which wire is which. SO if you connect the negative the the auto frame, how would the radio be creammed by hooking another negative wire to the positive power line? Hooking the positive to the other wire will simply make the radio come on.
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Old 06-29-2010, 07:36 PM   #13
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Connect the wire you think is positive to the positive of the radio. Connect the negative of the radio to the metal frame of the vehicle. If you have the positive correct the radio will come on.
and if not the radio is ruined.

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You should know on the radio which wire is which. SO if you connect the negative the the auto frame, how would the radio be creammed by hooking another negative wire to the positive power line? Hooking the positive to the other wire will simply make the radio come on.
I don't understand this.

If the polarity of the hookup is correct the radio will work, otherwise it will probably be ruined.
If both radio wires go to the + terminal or to the - terminal there will be zero volts across the radio and it won't work and won't be ruined.
These two paragraphs cover all four possibilities.

If the question is really about where the white wire and the black wire go inside the radio and there is no literature available on the radio
then
the OP needs to find the 'ground bus' on the printed circuit board inside the radio and use an ohmmeter to find which wire goes to it.
If the - terminals of electrolytic filter capacitors
http://www.electro-dan.co.uk/subwoofer/capbank-1.jpg
go to this bus, then that is the negative terminal.
You kind of have to know what you're looking for.

Last edited by Yoyizit; 06-29-2010 at 07:38 PM.
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Old 06-29-2010, 10:00 PM   #14
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DC power cord question


I thought he knew where the positive was on the radio. It was the adaptor he was trying to figure out. Unless the radio is some very odd configuration the metal frame will be the negative.
Post a make and model of the radio. Maybe we can find the plug configuration.

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