12v DC Light Wiring

[d30gaijin]

I just ran into a dilemma, I think. I wired up three over head double fixture 12v DC lights (switch on the light). There were no instructions that came with the lights and no indication I could find on them which wire is ground and which is hot. The wires are black and white coming out of the lights. Typically, with USA 12v DC, I am used to black being the ground wire so I presumed that the white would be the hot wire and wired them accordingly (I bought the lights at my local Camping World store) http://www.campingworld.com/shopping/product/12v-dome-lights-double/6124

Today I bought a single fixture porch light of the same brand (Gustafson) and while preparing to install it I noted, looking at the back (mounting) side of the light, that the white wire appears to be the ground wire since it is riveted to the aluminum base-plate that attaches to the trailer exterior wall and the black wire runs to the center contact on the bulb. So now I'm wondering if I wired the double fixture 12v lights backwards.

Is anyone familiar with the Gustafson 12v lights and which wire is ground (white?) and which hot (black?)??? The lights are made in Taiwan so perhaps their standard is different than the USA standard for what color represents ground? Any thoughts?

Thanks for any help you can provide.

Don

[George Taylor]

The color of the wire usualy does indicate hot or ground. But I have found that different manufactures will use different color combinations. What ever wire goes to either the metal frame/backing of the light or to the outer shell of the light buld holder is the ground.

[Ageless]

With the first set of lights; since the 'ground wire' wasn't rivetted to the base; it really won't matter. Incandescant lights don't care about polarity. Now when you get into LEDs; polarity matters.

[S. Heisley]

I wired my Gustafson porch light with black as positive (hot) and white, as negative, which is how I wired all my lights and outlets and it all came out fine. I don't have any LED lights yet.

Additional info:
It is important to remain consistent with your wire colors so that you or someone else does not get confused later. Some of my wiring is sound wire, which contains one black and one red. Wherever I used that, I simply identified the red as negative by adding white tape to it. But, the black remained as the constant positive or 'hot' wire everywhere.

I also identified my wire lines with colored tape so that no matter where I look, I can tell what wire belongs to what electrical run. However, I only used white tape to identify the negative wires and not to identify any electrical run. ...I hope that makes sense to you.

[d30gaijin]

With the first set of lights; since the 'ground wire' wasn't rivetted to the base; it really won't matter. Incandescant lights don't care about polarity. Now when you get into LEDs; polarity matters.

Ageless,

I would tend to agree with you about polarity for incandescent lights assuming they are all wired the same on one circuit, but won't it make a difference if three are wired one way and a fourth wired the opposite on the same circuit? If the assumed the hot wire for three lights are grounded and the hot wire for the other one is to the hot circuit something is going to give, I think, and that would be fuses or melted wires? And my goal is to eventually replace incandescent bulbs with LED bulbs.

Thanks for you help,

Don

[d30gaijin]

I wired my Gustafson porch light with black as positive (hot) and white, as negative, which is how I wired all my lights and outlets and it all came out fine. I don't have any LED lights yet.

Additional info:
It is important to remain consistent with your wire colors so that you or someone else does not get confused later. Some of my wiring is sound wire, which contains one black and one red. Wherever I used that, I simply identified the red as negative by adding white tape to it. But, the black remained as the constant positive or 'hot' wire everywhere.

I also identified my wire lines with colored tape so that no matter where I look, I can tell what wire belongs to what electrical run. However, I only used white tape to identify the negative wires and not to identify any electrical run. ...I hope that makes sense to you.

Sharon,

Thank you so much for your response. That is what I eventually suspected (black is positive). I will rewire the three over head lights accordingly, a pain but I am glad I asked here first rather than electrifying the circuit and finding out the hard way I had it backwards.

Oh, and your wire designation scheme makes perfect sense to me.

Again thank you,
Don

[Engineer Guy]

Having torn apart and wired up everything under the Sun since Rotary Phones and Vacuum Tubes, I got 'educated' on Auto Stds a few years back. My '83 Avion Land Yacht developed a dead Furnace. The Schematic showed - ta da - Black as hot +12 VDC and White wiring as Ground. Say what? Further work with 'Dinosaur Electronics' to retrofit their neato Control Board onto this Furnace drove home the fact that, in Auto Wiring, that's convention re: Color Coding.

I've been to Taiwan, and they're simply knocking out, on the cheap, lighting as specified by the parent Company. Wiring convention in Taiwan is the same as the U.S..

You'll likely dodge a bullet cuz Diodes 'block' reverse connection and current intrinsically. No current flow = no meltdown and no heat. With a Voltmeter, set Resistance to several hundred Ohms. The Red Voltmeter lead connected to the positive +12 VDC LED lead [correct polarity] will read 'low' Ohms. A reversed connection, connecting the LED light backwards, will read 'infinity' cuz no current will flow at all [reverse bias]. In this manner, you'll confirm LED hookup polarity non-destructively in advance. On lotsa Voltmeters, there's a lil Diode symbol. That setting is to be used for checking Diode integrity and polarity, light emitting or not.

http://www.allaboutcircuits.com/vol_3/chpt_3/2.html

In 230 VAC wiring where there's 2 'Hots' and 1 'Neutral', lotsa Electricians mark one hot lead with Red tape Then, they always connect it to the same lug on 230 VAC receptacles for Dryers, Stoves, Welders, etc.. Use the same on your wiring to follow the sound advice given above. Most folks will understand that Red = +12 VDC hot.

[Btennison]

In U.S., DC circuits conventionally have black/white wires with black always hot and white always neutral/gnd. In a 2 wire circuit where the only wires are black & red, the red wire is always hot.

In AC circuits white is neutral/common, black is hot. If "earth ground" is present it is either green or bare wire. Sometime with multi-phase there are two "hots" (red & black) and one "common" (white).

After that, it starts to get complicated.

Bob T

[Corwin C]

I don't trust colors ... the manufacturer (unless they document the colors) could be using any color to represent anything. I have purchased two identical lights in the same store at the same time, one light was white/blue wiring the other was yellow/green. The documentation stated that the light colored wire was ground and the dark hot. Go figure ...

Simple incandescent lighting does not care what the polarity is, however, conventional wisdom would be to make the "socket" the bulb goes into (-) or ground and the "tab" or "tabs" at the bottom of the socket would be (+) or hot. I have even ran into exception to this "rule" (some Volvo large trucks use a "positive ground" system on their headlights, the bright/dim switch is actually on the ground side of the circuit.) These connections and the polarity are easy to check with a multimeter ... I would recommend a multimeter to anyone wiring a trailer. Consistency is key. If you wire one light fixture one way, all of the other fixtures on the trailer should be wired the same way.

LED lighting, on the other hand, will be polarity sensitive (unless a correcting circuit is built into the fixture.) Again, documentation should explain how to wire them properly.

[BPFox]

I know i have said this before and some folks get mad at me, but it really does help if you think about it. Number one, there is no such thing as a "ground" wire in 12V DC wiring. You only have a 12 V positive wire and a 12 V negative wire. The term "ground" is used to indicate that you are using a "frame" as a common conductor for, in most cases, the negative wire. (ths is a long excepted misuse of the term "ground") The other thing to understand is that electricity is color blind. It can't tell what color the wire is. The only thing that matters is what colors are used at the source and that you stay consistant. In my business, which involves DC powered construction equipment, most of the time all of the wires are the same color and circuits are identified with numbers. Because of this, it's hard for me to wrap my head around the terms "hot" for positive and "ground" for negative since in DC wiring both the positive and negative wires are "hot" and neither of them is "grounded".

Now that I have said all of that, if you always use the wire that goes to the frame of the light as you negative wire and always use the wire that goes to the center of your bulb as the positive wire, it will never matter what color those wires are and you will never have a problem.

[Dale M.]

....... (some Volvo large trucks use a "positive ground" system on their headlights, the bright/dim switch is actually on the ground side of the circuit.) ......... Consistency is key.........

Notice any inconsistency.....

Dale

[Btennison]

... since in DC wiring both the positive and negative wires are "hot" and neither of them is "grounded".

Now that I have said all of that, if you always use the wire that goes to the frame of the light as you negative wire and always use the wire that goes to the center of your bulb as the positive wire, it will never matter what color those wires are and you will never have a problem.

Which is exactly the reason half the older cars in the world have a rats nest of multi-colored wires that don't match any code or even common sense.

I think most of us here realize our trailers are not "earth grounded" with a long extension cord. We use the terms "ground", "common" & "neutral" to denote the wire attached to the "-" (negative) terminal of the battery in a standard negative grounded system.

I don't see the necessity to get overly technical here. Suffice to say the "gnd/common/neutral" wire is usually white; the "positive/+12 VDC wire is usually black, sometimes red. Turn signals, brake lights and other special circuits can be any color (except white) and can have stripes denoting color.

Bob T

[kstephenson]

Wow.... seems like another subject going way over board on info. LOL
1. 12 V dc circuits use a (+) positive feed and a (-) negitive feed.
2. The color of the wires do not mean anything..... depends on the manufacturer of the component.
3. (+) positive is connected to battery (+) and (-) negative is connected to battery(-). .....yes we know it doesnt go to earth ground......but we accept the fact that for decades it has been called ground.

Hope I havent stepped on any toes again.....but lets keep it simple.....its not rocket science....haha

Happy Camping

[BPFox]

Just a couple of points. I did mention in my post that the use of the term "ground" was a commonly excepted term. Even if it is the wrong term, it its commonly excepted. That said, when we begin to use the terms, ground, common our neutral to mean the same thing, that is where confusion sets in. Those three terms mean three differnet things. and and I think it's a good idea if you know the difference.

My point is if you know what the wire is and you know what the wire does, it really does not matter what color it is. It is good to understand this because there is no standard for color use in direct current wiring. Heck, even the "ground" wire changes colors in most vehicles. It starts out black and by the time it gets to your trailer it''s white. Somebody way smarter than me is going to have to explain that one to me.

[Engineer Guy]

My hunch is that the term 'ground' dates back from REA electrification in the 'olden' days or the Tesla vs. Edison days when 'ground' was, indeed, the return path for current.

http://www.allaboutcircuits.com/vol_5/chpt_2/2.html

The Battery black lead used to not be grounded to vehicle frame until a braided, un-colored strap tied it to the vehicle frame. So, per the color codes fine points above, the Battery is 'ungrounded' until this final strap was connected.