There is a center pin, and two outside tabs. Which are positive and negative?

  • Ground outside... in most cars. – Sampo Sarrala Oct 23 '12 at 7:45
  • Seems like this information is also in en.wikipedia.org/wiki/DC_connector. – Sampo Sarrala Oct 23 '12 at 7:47
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    @Sampo: "ground" doesn't tell you anything about polarity, e.g. there are cars where the battery +ve terminal is connected to the chassis (i.e. positive ground). – Paul R Oct 23 '12 at 7:59
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    @PaulR sorry about that, my mistake. I meant negative by ground. In cigarette connector negative should (probably there are exceptions too) always be outside no matter how grounding is done. – Sampo Sarrala Oct 23 '12 at 8:02
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    A voltmeter is a handy tool. Pick a decent one up for $5 from Amazon. – Kris Bahnsen Oct 23 '12 at 20:49
up vote 29 down vote accepted

Every car that I have seen had center-positive cigarette lighter 'sockets'.

All (as far as I know) modern cars use negative ground systems, so the outer negative 'body' is vehicle ground and positive center is battery

You would expect this polarity to be maintained even with positive ground vehicles made by any sane manufacturer (and most insane ones as well).

AFAIR some old British Vehicles and Volkswagens had positive ground systems. No doubt there were others.

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    Ditto for me. Every car I've seen had positive on center pin. But I always put a protection diode in all devices that I made that needs to be powered from those sockets. Better safe than sorry :-) – Axeman Oct 23 '12 at 8:39
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    To @Axeman's point, if you can afford the voltage drop just put in a bridge rectifier -- that way it doesn't matter which input wire is which, you'll get +V where you expect and GND where you expect. – Doktor J Dec 24 '14 at 17:58

protected by Dave Tweed Mar 23 '15 at 12:15

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