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Wire pos or neg?

Old 06-14-2013, 05:03 PM
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Default Wire pos or neg?

Ok I have a slight problem, I have 2 black wires that go into my battery area are spliced and have a terminal to hook up to my battery, but I don’t know if it is positive or negative. I know black should be negative in a 12 volt system. But my friend that took the batteries out to charge them SWORE that it was connected to the positive, the marina installed my batteries and I don’t know where it goes. So my idea was to hook up an ohms meter on it and remove my dash and check the wires that go to the switches, wrong! I did this and the needle moves with every wire I touch under the dash, on both sides of the switch. How can I figure out if this wire is positive or negative???
Old 06-14-2013, 05:11 PM
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Safest way is to ring them out/trace them. I had the same problem on my boat. The previous owner wired his down-riggers starting at the down-rigger plug, realized he used wrong terminal there so reversed terminals at fuse panel. idiots abound.
Old 06-14-2013, 06:23 PM
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X2. Follow the wires. There has to be some access points. Is the black wire you referring to, a large thick wire going to the battery switch?
Old 06-14-2013, 07:29 PM
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I have tried to follow the wires, and can't, they run into tubes and can not follow them after they leave the battery box, I have the 2 positive wires goign to the switch, 1 negative going to the motor, then I have these 2 black wires both on the same battery ring, probably around 16 gauge, same size that runs to the dash switches, the thing is, everything seems to work, and it is wired in because when i tested it every place tested that there was conductivity
Old 06-14-2013, 09:09 PM
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Is the wire disconnected now? Are you hesitant to hook it up to the positive side because it may fry something? You might try to install a low blow fuse between the battery and the ring terminal. It is possible that who ever added the wire ran it in black because they did not know any better. It is common in house hold 120V to use a black as a hot or positive. I think the new ABYC code for 12 v positive is Yellow.
Old 06-15-2013, 05:16 AM
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Yes, I don't want to blow anything or fry gauges or anything, my gut tells me it's a ground because everything works and when I connected it to the ohms meter and started poking around it showed connectivity on everything, but I want to be sure before I leave it on my mooring.
Old 06-15-2013, 05:35 AM
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If you dont know the voltage of the wires, and you are not an expert multitester user, then follow this simple instructions:

I am assuming you have a single Battery system, or All Batteries have their GND/NEG post connected to a common GND cable (no need to know the exact cable). Bottom line, all battery or batteries are properly GROUNDED!

I am also assuming that the Cable in question is either Negative or Positive but not disconnected (not connected to either Pos nor Neg - could be switched).

Step1: Get a non-LED light bulb (LED bulb will require extra work).
Step2: connect 2 long wires to the bulb; test if the bulb actually works (remember the brightness)
Step3: Connect one of the wire of the bulb to the NEG post of a battery, any battery (assuming all batteries are grounded)
Step4: Connect the other wire of the bulb to the cable in question:

Bulb Lights up = The cable in question is Positive
Bulb Does not Light up = The cable in question is Negative or no Power

However if it lights up dimly, you have a wiring problem.
Old 06-15-2013, 05:38 AM
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Put the wires on the negative and see if everything on the boat works.. If not, remove the switch/panel and check from your unknown wire to your non operating wire pulled off of the switch. Usually the positive is the one thats broken with the switch, and there you have it.
Old 06-15-2013, 05:43 AM
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Simply ring it out to your engine block with every thing off..
Old 06-15-2013, 07:31 AM
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Originally Posted by freeporttuna View Post


Simply ring it out to your engine block with every thing off..
An issue would be that the GND probably meets up at the battery, so it might not ring to the engine block.
Old 06-15-2013, 08:42 AM
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Dekegill: Do you know what it means to ring a circuit? If so ignore the following.

See http://www.globaltestsupply.com/c/116/Extech_TG20_Wire_Tracer_Kit.html?gclid=CLjAucKx5rc CFUOi4AodJwcAgQ This is one of the cheapest "Fox and Hound" type tracers I've seen. It consists of a transmitter that sends an RF signal on a single wire it is connected to, and a receiver that listens for RF. The receiver has a pointed probe you can poke around with. When you locate a wire that carries a louder "warble" than anywhere else, you are 80% sure its the other end of the wire the transmitter is connected to.

Why not 100% sure? Because its a boat!
Old 06-15-2013, 07:43 PM
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Thanks for all the help, I bought that tool about a week ago to find the problem and it has not worked to find the problem, it is a 2 battery set up with both a common ground, I just got back from my mooring ( summer cottage 2 hours away) now that I thought about this the whole ride home, I never check the wires that go to my t-top, VHF t-top lights are up there. Everything worked great, other than when I flipped my t top lights on my radio (stero not VHF and not in t top) would die for 3 seconds then come back on.... I only get up there for the weekends, so I will try a lot of these sugestions next weekend, thanks for the help
Old 06-16-2013, 04:29 AM
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Hook things up without that wire and see what doesn't work would be another option.
Old 06-16-2013, 02:13 PM
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Both sides of switches will be positive as they are not the loads.
Use your multimeter/ohmmeter with one probe on the wire terminal in question and check with the other probe at only the positive bus or the negative bus to check for continuity or switch to volts and use a clamp on probe from the meter common to battery negative post.

If that reads positive 12vdc then the load is switched on and the wire should be connected to the battery switch common or if it is a bilge pump flat circuit + wire connect to battery positive or battery switch battery terminal.

If it reads nothing , it may be a negative wire or the load is not switched on.

In any case if it is indeed a positive connection wire, make sure the terminal insulation and a few inches of the wire leading to that terminal are clearly marked with red to show it is actually positive- either replace the ring terminal after slipping on re heat shrink, or "paint" the wire with red "liquid electrical tape" or wrap it with red self-amalgating tape. Better yet, after doing that also apply a printed label describing the load it is powering.

There should be an appropriate size fuse or breaker on any positive supply wire , within ~~8" or so of the battery or battery switch it is connected to, in order to protect the wiring ( not the load device.)
Old 06-16-2013, 04:28 PM
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Fuzes and breakers are on the positive side of accessories. Turn on the master switch, turn off all accessory switches, then see which battery terminal wire the fuses and breakers have continuity too. That's yer positive. Use the continuity test setting on your ohmmeter, which gives you a buzzer when the circuit is complete.

This diagram may help you to visualize it.

Last edited by Ed54; 06-16-2013 at 04:40 PM.

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