# Car cigarette lighter adapter. Pos/neg????



## James m

OK going to try hooking up an old CB radio. The cigarette lighter adapter had a sticker for positive and negative but it was lost. I have an electrical meter that I will turn onto ohms to see which wire goes through. But I need to know if the front is positive or the side is positive. Thanks in advance.


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## CWOLDOJAX

Don't set your meter to ohms.
Set it to vDC under 50 volts.
What is the the make/model/ year of the vehicle ?
European autos use a positive (+) ground and U.S. /Asian autos use a negative ground.
If I recall, the sleeve of the lighter socket is ground and the power wire is at the center of the back of the socket.


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## 8301

If the voltage (somewhere around 12.6) shows a neg symbol you've got the meter's hot lead touching the ground and vs versa. Swap the leads so there is no - symbol on the display and you know you've got the pos to the pos.


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## James m

It's not the cars adapter I'm having trouble with, its the wire side leading from the adapter you put in the car to the radio. It's an older radio that was supposed to be hard wired. I want to have the power to the radio go through the cigarette adapter. Sorry I didn't clarify. The part that goes in the car adapter, the front or side us positive?


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## James m

I assume the side with the glass fuse on the front would be positive.... I didn't think of that until I posted this. Duh on me.


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## tinkerhell

interesting question. I'll assume that you nothing. My apologies is that is not the cassette.

You will need a volt meter to read the cigarette lighter socket. I could tell you what the standard is, but that is something you can find in any maintenance manual. Definitely measuring is better than trusting a manual. (once you learn how to use your volt meter which ill go into in a bit.

Secondly, you will need an ohm meter to figure out your wire harness. Especially if both wires are black. The ohm meter will allow you to measure resistance on anything that isn't powered. If it is powered, you may get false readings and possible damage the meter.anyway, use the ohm meter to find which wire is connected to the center of the adapter 

When a meter is set to measure volts, you can practise measuring volts on any battery(make sure it is not a dead battery). You should not that matching the red probe to to positive side of a battery gives you a positive voltage measurement. When measuring the 12 volt socket, pay attention to the polarity otherwise you could get the wires reversed

Finally, get some fuses for you vehicle, if go shoving 2 probes into the 12volt socket, you are bound to cause a short and blow a fuse.


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## paraquack

I'd run my wires directly to the battery. Unfortunately if you for get to turn the CB off, you kill you battery, maybe. But it is the best connection for a radio.


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## PaulS

If you have the plug that goes into the cigarette lighter then the front/center post on the plug is positive and the outer ring is negative. (for US cars from about 1955 on)
Which wire from the radio you will have to get a wiring code for the specific radio. They can usually be found on the web or you can go to a place that installs radios and ask for the wiring code.


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## cdell

The center pin is positive and the outer edge is negative for vehicles manufactured for the North American market.


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## jimb1972

cdell said:


> The center pin is positive and the outer edge is negative for vehicles manufactured for the North American market.


Center hot side ground, there were only a few (I think British) cars that were positive ground.


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## GTGallop

jimb1972 said:


> Center hot side ground, there were only a few (I think British) cars that were positive ground.


Correct - The pin or spring loaded center contact is your positive. You can validate because it is probably fused inside the plug.
The neg or ground is the side contact and usually grounds out to the dashboard support metal behind the dash or grounds to the firewall. In either case it is a sufficient ground but also a poor ground.

Go straight to the battery and avoid going near the alternator. A CB draws minimal power when it is just listening - especially the newer ones that are all microprocessors and stuff. This way you can shut off the engine and wait silently while you listen / chat. That is the way I was set up with a Cobra WXSTII. Battery would last more than 24 hours with the radio on and still turn the engine over. Sometimes I left the radio on on purpose so would be thieves would hear the radio chatter and maybe think twice.

What kind of CB are you hooking up and what kind of antenna are you running?


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