Dumb question of the day... cig lighter

which is the center wire in a cigarette lighter? Pos (red) or Neg (black)?

unfortunately i am putting one on a boat and i don’t have an existing one to check to get the polarity right.

thanks, john

The center is normally positive, the wire color depends on your car.

The lighter doesn’t care. You can hook up the center wire to either Pos or Neg, and the case goes to the other pole.

What does matter is the normal grounding of your chassis. All contemporary automobiles use negative grounding and the lighter’s case is grounded through the chassis. So the center wire MUST be attached to Pos. If the dash on your boat is not grounded you can go either way, but it’s still conventional to attach the center wire to Pos.

Edit: Oops, I assumed you were to use it simply as a cigarette lighter. Nowadays these things are used as a power supply as well. Many accessories demand the conventional polarity. Therefore, always attach the center wire to Pos.

thanks for that. exactly, im putting about a grand of navigation software on a laptop so i DONT want to blow it out.

i was just having a brainfurt about ground. appreciate it.

I just did pretty much the same thing to install a “portable” GPS. I wired an auxiliary “cig. lighter” socket under the dash so I could semi-permanently install the power cord to the location where I velcro the GPS unit to the dash. That way I didn’t have to hack up the cord that came with the unit and I don’t have wires strung all over the cabin.

If you will be using an inverter and the power supply that came with your laptop computer, you will be safe with the DC outlet hooked up in either fashion. Look at the power cord for the laptop. It probably has a section that connects the black box to the AC outlet. That connection that plugs into the black box is usually reversable and the inverter will add additional protection. That is not to say that you should not bother to connect it the right way, but I am 100% sure your laptop computer won’t know the difference. If the inverter functions normally, the computer is safe.

That sounds like doing it the hard way. I just use one of these for 120VAC/12VDC/airline power connectors/etc.:


all the other electronics aside, some of the guys want to be able to plug in their car chargers for cell phone use too. (and I want to plug in the XM satellite too!)

since i needed to put a 12 volt power buss in, i figured i’d add the cigarette lighter. BUT, since it is going to be used by everyone in the wheelhouse I wanted to make sure it is wired correctly.

I want to make sure I am not responsible for blowing out any personal electronics. Thus the OP, for info.

thanks again, it works FINE now. BTW, why do lighters from Napa NOT come with wiring instructions?

You just put a test light to work. If it lights then the wire is positive. Couldn’t be easier.