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Old 15-03-2015, 16:14   #1
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Hopefully a simple 12v question

We are electrical novices, although we've read the section about electrics in our Don Casey books.

Today we went to the boat to try to wire a small computer fan (less than 2 amps over 24 hours) into the circuit that currently has a cigarette lighter on it.

When we opened up the fuse panel (it's an old boat, so it has fuses, not breakers), we realized we had no idea where or how to make the connection. The green wire in the picture below goes to the cigarette lighter. Where would the negative and positive leads from the fan connect onto this?






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Old 15-03-2015, 16:26   #2
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Re: Hopefully a simple 12v question

There are normally TWO wires to the cigarette lighter?
Normally the one to the outside case is - and the one to the centre at the base is +. Connect your fan to the same two wires - if the fan goes the wrong way, reverse the wires.
If you wish to learn more, put a multimeter set on a suitable DC range across the wires - it will read the available voltage, and, if the red lead on the meter is on the - side, there will be a - sign in front of the voltage.
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Old 15-03-2015, 16:37   #3
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Re: Hopefully a simple 12v question

I don't know if there are two wires to the cigarette lighter. The cigarette lighter is attached to the green wire. We're just trying to use that same circuit for the fan. We bought wire for the fan, and can't figure out how and where to attach that wire onto the panel.
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Old 15-03-2015, 16:43   #4
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Re: Hopefully a simple 12v question

There has to be a circuit. A circuit requires both a + and a -. If there is only one wire, the mounting of the cig socket must be part of the circuit. Easy to check. Put one wire from the fan onto the terminal of the green wire, and the other to the frame of the socket, or the mount. Does it go?
If you have a multimeter, set it to DC, range to 20v, one probe on the green wire, one on the mounting or socket frame. Does is display voltage? Move the 2nd probe around the various connections if not, until you see a voltage.
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Old 15-03-2015, 16:45   #5
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Re: Hopefully a simple 12v question

There must be a ground bus where the other wire from the lighter socket is attached. The bus then connects to the battery negative (-) terminal. If you have a current monitor there will probably be a shunt resistor between the battery negative and the ground bus.

And please, get rid of the wire nuts. Use a terminal strip for the connections and crimped lugs on the wires. If the existing wires between the wire nut and the switches are too short, get a soldering iron and replace them with longer wires.
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Old 15-03-2015, 17:30   #6
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Re: Hopefully a simple 12v question

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Originally Posted by Neptune's Gear View Post
There has to be a circuit. A circuit requires both a + and a -. If there is only one wire, the mounting of the cig socket must be part of the circuit. Easy to check. Put one wire from the fan onto the terminal of the green wire, and the other to the frame of the socket, or the mount. Does it go?
If you have a multimeter, set it to DC, range to 20v, one probe on the green wire, one on the mounting or socket frame. Does is display voltage? Move the 2nd probe around the various connections if not, until you see a voltage.
We're definitely going to get a multimeter. In the meantime, if I'm understanding this correctly, are you saying that we would splice it from the wires near the cigarette lighter as opposed to near the panel?
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Old 15-03-2015, 17:36   #7
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Re: Hopefully a simple 12v question

the pos of the fan goes into that green / black connection. I would add a small 1a fuse inline with the fan wire. otherwise the fan is only protected by the larger (probably 15a fuse) from the cig plug.


you need to find the ground bus for the neg. the cig plug has to have 2 wires. follow the other one.
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Old 15-03-2015, 17:37   #8
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Re: Hopefully a simple 12v question

A little confusion here. Are you planning on locating the new fan where the old cigarette lighter is or will you be pulling new wires to place the fan in a different location?
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Old 15-03-2015, 17:43   #9
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Re: Hopefully a simple 12v question

One of the basics that I continue to note is that pictures of wiring without an electrical diagram are useless in trying to help OPs.

The skippers are right, you need the tools and the TIME to draw a wiring diagram and find out what you really have.

Yes, you can wire it to the lighter's studs, but wouldn't you wanna know what's really happening in there?

None of us were born electricians, we all learned the hard way. We bought a book or two or found one on the internet. Charlie Wing's one is very good for just the issues you face.

The mitigating issue is that whoever did what you pictured appears to have used GREEN wire for a DC circuit.

That's plain wrong, so it's hard for us to tell you what to do.

Other than learning about how it SHOULD work and then drawing up what you ACTUALLY may have back there.

Your panel is one of the simpler ones, and many "beginner" electrical books cover just these issues.

BOOKS

Every so often folks ask: "What book should I buy to learn electrical stuff about my boat?"

The appropriate answer is: "Depends on how you like to learn."

Go to a chandlery and read a few in person, and start by buying one that you think suits your "level" and is "readable" to you."

A good starting list is provided by West Marine in the their online Advisors (and usually in their catalogs, one of which should be in your house and the other on your boat).

Recommended Books on Marine Electrical Systems | West Marine

Happy Hunting.

Good luck.

You'll appreciate the improved knowledge of what it is you have.
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Old 15-03-2015, 17:49   #10
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Re: Hopefully a simple 12v question

And get rid of the wire nuts. They are definitely not intended for a marine environment.
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Old 15-03-2015, 19:14   #11
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Re: Hopefully a simple 12v question

Thanks to everyone for the advice and suggestions. It's becoming a bit more clear.

We definitely want to learn about this - not just how to do it - but we also want to get this wired before we splash in six weeks. We've ordered Nigel Calder's book and will be diving in when it arrives on Wednesday. Hopefully we'll have a bit more success when we go back to the boat on Saturday.

And yes, the wire nuts will eventually be gone.

Thanks again.
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Old 15-03-2015, 19:27   #12
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Re: Hopefully a simple 12v question

Just a cautionary note. Most fires on boats are started by electrical faults. Do learn how to do wiring installs properly.
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Old 15-03-2015, 20:04   #13
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Re: Hopefully a simple 12v question

6 weeks sounds a very short period of time for a clearly starting cold electrical novice to rewire a boat. Not likely to be a good outcome.

Second concern: the fuse rating for the cigarette lighter is likely to be 15 amps or more. The wiring on a dc fan may be good for only 5 amps or less so there is a very real fire risk from the proposed combination.

I rarely say this, but from the nature of the question I suggest a professional should be involved. There is simply not enough demonstrated understanding to do this safely in my opinion.

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Old 15-03-2015, 21:06   #14
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Re: Hopefully a simple 12v question

We're not trying to rewire the entire boat before we splash.

We're about to start our third season on the boat, and up until the middle of last season the only thing we used the electric for was 1 or 2 LED cabin lights for approx 10-15 minutes at night, and of course the electric start on the outboard.
We then purchased a Nature's Head which has a small computer fan (less than 2 amps over 24 hours) for which we used a temporary splice off of one of the LED lights. Now we'd like to remove the splice from the light.

We read the relevant Casey chapters, bought 16 gauge marine grade wire to use instead of the cheap wire that came with the fan, and were caught off guard when we removed the panel and didn't see positive and negative wires like we thought we would.

I'd like to think that with the help of our books, plus the Internet, we can figure out what should be a reasonably simple task within the next week - let alone six - without calling in a professional.
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Old 15-03-2015, 21:21   #15
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Re: Hopefully a simple 12v question

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We read the relevant Casey chapters, bought 16 gauge marine grade wire to use ...
Yikes, too small. I never use anything less than 12 ga on my boat, some use 14. Check again.
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