Whoops I forgot to label the wire.

[Gina Marie]

Help when I was painting my under cockpit area I disconnected a single 12 volt battery. I think it goes to my generator. I took the wires off the battery and did not mark the colors as to what is + or - . The wire is a two conductor it has a white and a black lead. The white goes directly to the battery and the black goes to a battery switcher and continues out of the switcher in a black sheath. Is black positive. Help!!!!!!! thanks.....

 

[CUBANCIGARS]

HI
i'M NOT A BOAT OWNER, BUT A GENERAL RULE OF ELECTRICAL REPAIR IS THAT THE WHITE GOES TO EARTH OR THE (-) SIDE OF THE BATTERY WITH THE BLACK FLOWING THROUGH A SWITCH. YOU CAN CHECK THE POLARITY BUT RUNNING A SINGLE WIRE FROM THE OTHER SIDE OF THE BATTERY MARKED WITH A (+) AND CONNECT A SMALL LIGHT BULB (12 VOLT) TO THE ENDS OF THE WIRE. IF THE LIGHT WORKS YOU HAVE A BOTH (+) NEW WIRE AND (-) OLD WHITE WIRE. IF THE LIGHT DOES NOT WORK THEN BOTH YOUR WIRES ARE COMING FROM THE SAME SIDE OF THE BATTERY, MAKE SURE YOU HAVE GOOD LIGHT BULB.
STEVE

 

[MikeP]

Black is negative in a starting circuit. However, since there is no telling what a previous owner may have done wiring-wise (assume they did it wrong because that assumption will usually be right) get a multimeter, put in on the ohms setting and connect it between the black wire and a known ground, like the engine block. If it is, in fact, a negative (ground) wire, you will get a continuity reading on the multimeter. If it turns out that way, connect it to the negative batt terminal.

 

[Gina Marie]

Thanks for the reply's . MikeP996 I will run a meter between the black wire coming out of the battery switch that is mounted to the wall and the block of the engine. If it tones I will attach to - Negative. Vis a versa if it don't.
Thanks again for the reply's
.

 

[Genesis]

Thanks for the reply's . MikeP996 I will run a meter between the black wire coming out of the battery switch that is mounted to the wall and the block of the engine. If it tones I will attach to - Negative. Vis a versa if it don't.
Thanks again for the reply's
.

The wire attached to the switch BETTER BE positive.

If its not, then whoever wired that did it very, very wrong (and dangerously so.)

Ground on a 12V system must NEVER be switched - only HOT.

The reason is the same with high voltage (e.g. 120V) service - you NEVER switch neutral, always hot.

Why? Because if you switch neutral (or ground) then there is a very real risk that someone will think the circuit is "off" when the switch is open, and end up shorting it to ground, producing major sparks (and in the case of a HV circuit, possible electrocution)

When high-current systems are involved (e.g. storage batteries) the result of that sort of miswiring and an accident can be actual electrical explosions or serious electrical burns - even with a 12V system.

White/Black is NON-STANDARD for DC systems. DC should be RED/YELLOW or RED/BLACK. White is the color for AC neutral and should NEVER be used in a DC system.

Tone it out - disconnect both leads of the battery, put meter on VOLTS, turn the switch on, and check each wire between itself and the case of the generator. NEITHER should show any voltage (always do this first before you do an ohm test - just in case - to keep from frying your meter!)

Then ohm each lead from the lead to the generator case. One should show open (infinite ohms), the other zero ohms.

The zero ohms lead is negative (assuming a standard, negative-ground system)

If that lead is the one that goes through the switch then fix the wiring, and while you're at it, change the positive to a RED wire (black is ok for negative, although yellow is better, as it cannot be confused with 120VAC HOT.)

 

[Gina Marie]

Genesis, I will takea meter to it tommorrow. Just so I understand. The battery at this time is disconnected. I have a white and a black that is going through a battery switch. I will first check voltage between both leads and a ground like the engine block. Assuming both are 0 ,I will then tone each wire. Once toned the one with the continuity is my positive lead which should be the switched now black wire.

 

[Genesis]

Genesis, I will takea meter to it tommorrow. Just so I understand. The battery at this time is disconnected. I have a white and a black that is going through a battery switch. I will first check voltage between both leads and a ground like the engine block. Assuming both are 0 ,I will then tone each wire. Once toned the one with the continuity is my positive lead which should be the switched now black wire.

Careful - that's backwards!

The one that tones to the BLOCK is your NEGATIVE wire, and should NOT be switched. The other one should show OPEN (no tone)

If the one you think is negative (shows tone to the block) runs through the switch, be extremely careful. It could be that someone did that, but it could also be that you've got it wrong and if you connect it backwards you'll get sparks at best and possibly severe damage or even a dead short across a battery through a very heavy cable (which can cause really bad things like explosions) at worst.

One of the leads, when traced, should go to ship's ground (e.g. an engine block or a common grounding bus bar.) That's the negative lead. That lead should NOT go through a switch.

If you find that the wiring is of the wrong color or the wrong lead is switched, and it sounds like at least one of these IS true, do yourself (and the next person who works on the boat) a favor and replace the errant cables. The wire isn't THAT expensive and this kind of screw-up is extremely dangerous, especially on primary (battery) cables.

If you're not ABSOLUTELY CERTAIN which wire is positive and negative after checking this, find someone to help you. This is not an error you want to make as the consequences of being wrong are very severe, including immediately destroying electronics, an electrical fire or even a battery explosion if there are other batteries on line at the time.

I'm curious as to what this battery is for. If its the only one and not related to part of a bank, it may be for something like genset starting. If so then it is almost certain that a previous owner added it, and if it was done incorrectly, you definitely don't want to be the one to get a "surprise" by making assumptions.

 

[Nonchalant1]

It is extremely likely that the one that goes to the switch is positive, but it needs to be checked to see. If you determine from a continuity test "tone" that the black, switched wire is positive, go ahead and connect that to the positive terminal, and white to negative. If you determine that the other wire is positive (i.e. negative goes to the switch) DON'T connect it that way. Call in some help.
If it's a "post" style battery connection, like a car, another point to check is that many 12V batteries have different size terminals for positive and negative. You may be able to tell that one post on the battery is larger than the other and that one of the terminal connections you took off is larger than the other, and fits only the larger post.

Doug Shuman

 

[Bob Bradley]

I've seen situations, both on my '65 Chris, and my '79 Hatt, where white/black is used in stead of black/red on 12vdc. It seems that in house wiring systems (not main engine starting system), the color coding changes to that of household wiring where black is hot, white is neutral or negative, and if present, green is ground. This may explain this apparent anomoly.
Bob

 

[Gina Marie]

Thank you all for advise. After metering the both wires before connecting the battery I had no power on either wire. The white wire proved to be the negative and the black wire was the positive which was switched. All went well and I am back on track Thanks again. This forum works!!!!!!!!!!!!!!!!!!!

 

[Traveler 45C]

All of my battery cables are black (except the ones that are painted white- overspray of course). I hate it. Before I ever worked on any part of the DC system, I traced out every wire and made a diagram. I found many changes from the original wiring diagrams that came with the boat. When I make a change to the system I annotate the diagrams that I made. This way I won’t forget what I did and the next owner will benefit.

 

[MikeP]

"Temporary" wire color changes

A common method of using the "wrong" color cable is to wrap the last foot or so of each end with the correct color tape. For example, if you needed to replace a black negative battery cable but had some appropriate sized red cable, you would wrap black electrical tape around both ends of the red cable as described.

This procedure is handy because you can quickly "color code" the wires for maintanance purposes, pending eventual replacement with new cables of the correct color.