Basic 12 Volt Wiring: How to Install a LED Light Fixture

This is the second in a series of posts covering 12 Volt Wiring Basics. In the first we installed a cigarette lighter plug. It was so simple that all we did was focus on stripping and crimping a wire. You may want to go back and review it before trying this installation. Find it here: In this post we are going to move up a step in complexity and install a LED light fixture. I bought this LED fixture from and I am extremely happy with it. It has 230 Lumens and comes with a light dimmer. On full brightness I can easily read by it, but at its lowest setting it is great to watch TV by. Best of all it only draws 3 watts which is incredibly little. That’s .25 (one quarter) of an amp. For only $15 I highly recommend it!! Find it here: Gold Stars LED Dome Light Fixture 230 Lumens 12v With Dimmer (I have the lens off so you can see the LEDs inside.)

230 Lumen LED Light Fixture With Dimmer Switch

230 Lumen LED Light Fixture With Dimmer Switch

Like nearly all 12 volt appliances, the fixture we are working with came with only two short wires. The fixture I have came with two white wires which confused me, so I did some research and found out that meant it was polarity neutral, so I could wire either wire to either positive or negative post of the battery. That made it simple. But other fixtures will come with normal red or black wires, and that is also simple because you just connect black wire to black wire and red wire to red wire and the red goes to the positive post and the black goes to the negative post of the battery. It just follows normal 12 volt automotive color conventions.

I places an arrow pointing out that it draws 3 Watts at 12 Volt.

I placed a red arrow pointing out that it draws 3 Watts at 12 Volt. Notice the 2 white wires.

Sometimes a 12 volt fixture will come with black and white wires and that creates a problem for most of us: which is positive and which is negative? In cases like that they are following the NEC Code which uses 110 volt wire color codes. In that case black is positive and white is negative (neutral in 110 volt terminology) So you would wire a red wire to the black wire coming out of the fixture and a black wire to the white wire coming out of the fixture and the black would go to the negative post and the red wire would go to the positive post. Here is a diagram to help clarify that:

Diagram showing which color wire to use.

Diagram showing which color wire to use.

The next thing we need to do is decide on a wire size. But, I don’t want to get too far side-tracked right now on wire sizes, so suffice it to say that based on my experience I knew that an 18 gauge wire would be big enough and confirmed it with a wire calculator. In a future post I will go through wire sizes and the use of a wire size calculator like this one: At that time I will explain wire sizes and how to use the calculator. As a very broad rule the majority of 12 volt items that you use will be fine with 14, or 10 gauges. Most things that need a bigger wire than that will come with the wire or with instructions in the manual for which wire to use. I generally go with a slightly heavier wire than is called for and I have a lot of 14 gauge wire on hand (I keep 14, 10, and 6 gauge wire with me all the time and if in doubt I go to the larger wire) so that is what we will use.

Before we do the actual installation, I want you to see a diagram of all the parts unconnected (exploded) so you get a visual image of the overall project:

An exploded view of all the parts and pieces before they are connected.

An exploded view of all the parts and pieces before they are connected.

Next we are going to use the basic skills of stripping and crimping that we learned in the last lesson.

Step 1: Strip and crimp a butt connector to each wire coming off the light fixture. Then strip and crimp a black wire to one and a red wire to the other. Since this fixture is polarity neutral it doesn’t matter which. Otherwise you would use the color codes I gave you above.

Butt connectors crimped onto the two white wires coming off the Fixture.

Butt connectors crimped onto the two white wires coming off the Fixture.

Step 2: Put the fixture where ever you are going to mount it and then run the wire however you are running it back to the battery. I buy the smaller wire in at least 30 feet rolls (from Walmart in the auto-electrical section) and in a van most runs are around 8-15 feet (or less) so I always have scraps left over. That’s what I used for this job.

Crimping a Butt Connector.

Crimping a Butt Connector.

Step 3: Strip and crimp a ring connector to the black (negative) wire.


The ring connector crimped on. With all your crimps, after you are done give them a good tug to test them and be sure they are secure.

Step 4: We are adding a new twist this time and we are going to add an in-line fuse on the red, positive wire. They usually come with a complete circle of wire so the first step is to cut it in half. Then strip and crimp a butt connector on one end and a ring connector on the other end of the in-line fuse. Then strip and crimp the butt connector coming off the in-line fuse to the red, positive wire coming from the fixture. Last thing; put either a 5 amp or 7.5 amp standard blade fuse in the fuse holder. Here is a 16 gauge fuse holder from In-line ATO/ATC Fuse Holder 16 AWG

 Step 5: Wrap all the connections you just made with electrical tape.

Wrap all the connections with electrical tape.

Wrap all the connections with electrical tape.

Step 6: Take the nuts off the battery terminals and put the black wire to the negative (-) post and the red wire to the positive (+) post.

The In-line Fuse (and red wire all the way back to the Light Fixture) attached to the battery post.

The In-line Fuse (and red wire all the way back to the Light Fixture) attached to the battery post.

Step 7: Turn on your new light and enjoy!

One thing you’re going to notice before long is that your battery posts are going to get very cluttered with wires from all the things you are adding. Next time we will look at how to add a fuse block to eliminate most of that problem.  

58 comments on “Basic 12 Volt Wiring: How to Install a LED Light Fixture
  1. Avatar Marshall says:

    Good job. Well simplified!

  2. Avatar randy(livinfree 1964) says:

    very good step by step,easy to understand instruction Bob!! I think you have found your calling!! Keep up the good work.we all really appreciate what you are doing.

  3. Avatar Richard says:

    Be aware that in older model travel trailers, it is very likely that the manufacturer has not adhered to any specific standard.

    In my 1969 Aristocrat, as an example, black is DC hot while blue is DC return (in most cases). Some times the DC return is white and sometimes it is yellow.

    • Avatar Bob says:

      That’s a great point Richard, I’m glad you made it! But my advice was for installing modern 12 volt appliances (which should follow the current NEC cord or standard 12 volt auto code) and wire them directly to your battery.

      I know so little about RVs that I don’t give any advice as to how to wire them or add anything to them like a light fixture or solar panel. The only way I will help someone with an RV is if we go direct to the batteries and not through any part of the RV electrical system. And your trailer is an example of why, you just never know what the factory did and I have such limited knowledge I can’t figure it all out.

  4. Avatar Mary says:

    Good clear descriptions. And I learned something – those pesky color codes. I hate how the colors are different for Ac and DC wiring.
    Mary recently posted…FailuresMy Profile

  5. Avatar Lisa says:

    Thanks Bob,
    I’m going to share your site with friends of mine. You covered some very important subjects with your recent posts and I learned a lot. The electricity part is something I would have to print out. Thanks for sharing name brands. Happy van dwelling.

  6. Avatar Bindi&us says:

    Hi Bob, very good tutorial. You offer a fine presentation for beginners, as well as for those of who have done lots of this stuff. (never know when I’ll pick up a good tip, such as today…great fixture find).

    Often I’ve used what we used to call zipwire (lamp cord) for light duty applications like this. Its easy and neat to run being basically 1 piece.
    One side of the pair is marked by either raised ribs or embossed with Mfg, size, etc. to denote polarity easily….neutral is the marked side for 120V.

    Hope you find this useful.

    • Avatar Bob says:

      Bindi&us, thanks for that tip! I’ve never really worked with 110 volt so I know very little about it. But that helps a lot to understand cords.

  7. Avatar Archie says:

    You give very good directions for wiring a light to a battery. However I need to find a wiring diagram for a 1999 Sandpiper rv. The 12 volt lights over my table and couch only have 1.3 volts in them. The lights are in the slide out on this camper and NO wires show under the slide out. I in all honesty have no idea what I am doing but I am slowly learning as I keep having to work on this camper.

    • Avatar Bob says:

      Hi Archie, I wish I could be more helpful but I know very little about RVs so I’m afraid I can’t help you. I suggest you join my forum and post this question there because there are many people there who are very knowledgeable about RVs.

      At the top of the page is a button that says “Forums” just click on it and join.

  8. Avatar Caroline says:

    Great info. I’ve lived off grid (in a couple houses, shhh) for the last 28 years and have just recently become a LED addict. My son gave me some simple 1v LED spots that I want to hook directly to my battery bank. Could I follow this guideline if the batteries are connected in parallel and series? It would be great to have them lighting up the generator shack when I have to start it after cloudy days.

    • Avatar Bob says:

      Hi Carolie, it doesn’t matter how the batteries are wired together as long as they end up being 12 volt. I’m sorry but I don’t know he answer to if you can wire a 1 volt LED to a 12 volt battery bank. That’s outside my knowledge base. But my best guess is no, you would need a resistor to bring down the voltage to match.

  9. Avatar Eric says:

    Great article. Sadly, this lamp isn’t available on Amazon any longer, but you should be able to find them on ebay for around $30, just search “9090101”. Strangely there don’t seem to be a lot of dimmable 12v LED lamps out there so this may still be the best one to go with.

  10. Avatar Bob Baar says:

    Love your website! My wife and myself are going to hit the road the first of the year and all your ideas are greatly appreciated as we are on a fixed income and need to save every way we can. I know we will use many of your suggestions. keep up the great work you do.
    Bob and Cher

    • Avatar Bob says:

      Bob, you are in for a real treat as you change your life! Don’t be surprised if there are some real emotional and mental adjustments you have to make as you change from the traditional life to the mobile life. It can be quite a shock! Hang in their, it’s worth it in the long run!

  11. Avatar Larry Campbell says:

    I am having a problem connecting my rv interior lighting.My rv has 3 wires 1 black and 2 white.My led interior I bought has 1 red wire and 1 black led light will not work at all.Any solutions.Thank you very much.Larry

    • Avatar Bob says:

      Larry, I hate to admit this but I know very little about RVs so I can’t help you. If you join my forum and ask this question there you will get TONS of great help from people who know RVs.

      To join, go to my website, and click on the forum button.

  12. Avatar Robert says:

    I have a question about a DPDT 12v relay, I want power to the NC circuit when there is no power to the coil so I can have a magnetic switch and a LED light come on when there is no power to the coil. Do I run a separate power supply to the NC side and then when the switch is activated the LED light should come on. Could you double check me about this please and let me know if this is right or tell me what to do.
    Your explanation of the relays is very informative and easy to understand.
    Thank you, Robert

    • Avatar Bob says:

      Robert, I’m sorry but you are way over my head. I understood very little of what you asked. I actually know very little about elctrical.

  13. Avatar becca says:

    did you ever make a post on putting in a fuse block?

  14. Avatar toni says:

    wat type of van should i get

    • Avatar Bob says:

      Toni, that is a very hard question to answer because all our situations are so different. But just to give you an all-around answer even though I know nothing about you and your specific needs, I’d say a high-top Chevy or Ford Conversion van. Buy it as new and with as few miles as you can afford.

      If you tell me a lot more about yourself and what your plans are I can give you an answer tailored to you and not a generalization. Here is an introductory post on the subject:

  15. Avatar larry says:

    in regards to your 12v description with a light fixture directly to battery. #1 can you add a simple 12v light switch to wall that turns light on and off?
    can the fixture be grounded to trailer frame right where it is mounted and the battery grounded to trailer frame where it is located? That way all you would have to string is one wire running from battery to switch and to fixture. Is this correct?


  16. Avatar Speedhut says:

    Good job Bob! Very easy and understandable step by step instructions. Continue sharing your information. It helps so much.

  17. Avatar Leif Madsen says:

    Hello Bob,

    Thank you for all of your information. I am getting ready to install a variety of 12 volt devices (LED Lights, Submersible water pump, etc.) and am using 12 AWG wire for all applications just to be safe. My question is, many of the devices came with much smaller wire (between 18 and 22 gauge) that I am supposed to connect the 12 gauge wire to using butt connectors. Does this difference in wire size matter? Or should I forget using the 12 AWG and use the same gauge wire extending from the device to run to my fuse block? Here is an example, I ordered a 12 volt plug from amazon and it came with a 22 gauge ground wire. That means I would be connecting a 12 gauge wire directly to the positive lead and then connecting a 12 AWG negative lead from the ground block to the 22 gauge ground wire that came with the plug. Is this normal?

    Thank you,


    • Avatar Bob says:

      Leif, for those you may want to use 14 gauge so they are closer in size. 14 gauge uses a blue connector and it will be closer in size. On the 18-22 gauge wire, you can strip off more of it and bend it over and wrap it around itself by twisting it so it is thicker and will fill the 14 gauge connector. You might also try wire nuts instead. Buy a variety kit and find a nut that just barely will take the two wires and use it.

  18. Avatar Linda Harris says:

    We bought a 2015 Silverback bunkhouse 5th wheel and in less than a year some of the ceiling puck lights started burning out. I replaced 3 of them and a few months later they started flickering and going out again. There are 6 of these over the dinning room slideout wired in series to a central switch. Both wires are black and the $20.00 replacement lights had 2 black wires. I am getting ready to order a pack of ten lights from Amazon but these have a black and white wire. Suggestion on how to connect?

    • Avatar Bob says:

      Linda, I’m sorry but I don’t know much about RVs and can’t help you. But if you will join my forum and ask this question there I’m sure you will get all the help you need. Go to my website and at the top of the page are menu buttons, click on the one that says Forums and then join.

      Sorry I can’t help you but I know they can.

  19. Avatar bleu says:

    Hi Bob, I’m putting a little dome light in my 64 Falcon Van. Thanks so much for the simple instructions, it’s exactly what I needed. Also, I have to say, your patience is impressive. I read thru your comments & am stunned at all the questions regarding RV’s. You always address them with such a gentle nudge towards the forum. Thanks for being so polite in a world where that’s gone out of style. God bless you

  20. Avatar Rachel says:

    Hi Bob, I was out on Google looking for answers about my lights and saw your site pop up. Thanks for the info on the black and white wires! That’s what my Gustafson lights have and it didn’t make sense to me either. I am so accustomed to black being negative, but the switch on the light is running through the black wiring. Egads! I found mine in a thrift shop, so there were not any directions. So. Black to red. Weird! But good to know. Thanks!

  21. Avatar Tom says:

    Hello Bob

    I’m hoping you can help me
    I’m in the UK and I have a enclosed box trailer with a 7 PIN plug

    And i want to put some lighting in there
    I just bought some 12v led lights on a roll 5 Metres long from eBay

    I wish to connect the lights to a 12v battery with a on/off switch (if possible)
    but the tricky part is I need the battery to charge whilst being plugged in to the vehicle and towing

    I have looked everywhere on the internet for days and I can not get a straight answer or a diagram or anything I’m not a expert on electrics
    hopefully you can help and ill be looking forward to your reply or anybody’s if they know

    thank you talk you soon
    kind regards Tom

    • Avatar Bob says:

      Tom, One of the 7 pins in your trailer connection is a wire to charge your house battery in the trailer. You’ll have to get the wiring diagram for the trailer and see where it comes out and wire your house battery to it. I’ve never done that so I’m afraid I can’t help you with it.

      I’m sorry, but I’ve never worked with the LED trip lights so I’m unfamiliar with how they wire into the system

      I’m sorry I can’t be more help but those are just things outside my experience.

  22. Avatar Dale Watkins says:

    Bob…I am replacing an old lamp with a new lamp (LED) Old one is one wire and a ground wire…new one has two wires…How do I connect the new two wire to the old one wire and ground…Maybe some out there knows…

    • Avatar Bob says:

      Dale, I don’t understand, they both have two wires, is that right? On both of them one is positive and one is negative. Is your question about color, is one red and black and one is black and white?

      • Avatar Dale Watkins says:

        Bob….the lamp is black and white….the wires n the ceiling are black and bare copper which was attached to the metal surface of the lamp i am replacing… so i assume the copper was the ground.

  23. Hye buddy…
    I really like your article…keep writing buddy!!!
    Thanks for taking all the time to share your experience and lay out all this info!!

  24. Avatar Art Gant says:

    I guess my question on the light is why not simply ground to the vehicle. All the vehicles own electrics are grounded to the frame and body. If your installing multiple lights and 12v appliances rather than using a buss bar, you can use a fuse block, run the grounds to the vehicle, and in the case of low amp draw lights and fan, you can run a single wire down the spine and tap into it with splice connectors, or run individual power from the fuse block to each appliance.

  25. Avatar Kathy C. says:

    Bob – I know you wrote this years ago, but this blog post is just as relevant today! I changed out two reading lights in my trailer and yours was the only place I could get information about the “two white wires”. It gave me confidence and the end result is a winner. Thanks so much for sharing your experiences and information and educating a rookie!

  26. Avatar Kyle says:

    So your link to the light fixtures no longer works. Would these work well in it’s place? I was particularly interested in your recommendation based on the low energy consumption of the lights.

  27. Avatar Kathy says:

    Bob, this post was written a few years ago, but just helped me immensely. Knowing nothing about electrical, the key line here “so I did some research and found out that meant it was polarity neutral, so I could wire either wire to either positive or negative post of the battery” gave me the confidence to plunge ahead. I could not find information about the “two white wires” anywhere online — except here.

    The new LED lights are working like champs, thanks to you!

  28. Avatar Nick says:

    Dear Bob,

    I have a travel trailer with 12 volt lighting throughout. The original fixtures required incandescent bulbs. I have since traded out ALL incandescent (inside and out) with LED which use a fraction of the power necessary for the incandescents. My question is this: Can I add one or two more LED light fixtures to an existing overhead light fixture? The trailer has black/white wire, and my little reading lamp fixtures have black/white wires. These little reading lamps only use 1 watt each. I don’t believe that these would overload the existing circuits. Any info would be appreciated. Thanks

  29. Avatar Monique says:

    Hello Bob,
    I made a mistake when replacing a burned out led light in our RV. When I disconnected the old fixture, the white and black wire touched, lightly crackled and then no lights within an area of the fixture. No breaker was tripped, nor any fuse blown in the box. Can you help me troubleshoot. As you know travel trailers are difficult to dig into ceilings to trace wiring. What kind of damage did I do? Help me troubleshoot please?

  30. Avatar Joshua says:

    I just got these off of amazon.

    Can I cut the wires with any pair or scissors? or do I need a specific kind to pair it up to my power?

    Thanks for the guide btw

  31. Avatar Dave says:

    Hi, Bob…I see it’s been a while since you last posted. Hope you’re still up & at’em.

    About a year ago, I bought an old prison transport bus (’89 Dodge B350 Maxi-van) to convert to a campervan for when I retire next year. Been working on it, off & on, and have the bed installed & kitchen mostly done, and have most parts for my electronics. Planning on a split-charging system with 3 90ah deep cycle batteries isolated with a Pollak kill switch to my starter battery (charging off the alternator when I’m moving), with a 100w solar panel (for when I’m parked). Since my electrical needs are fairly small, I’ll run my loads through a Blue Sea 6-way fuse block. Two 7-gallon Reliance Aqua-tainers will hold my fresh water supply, operated by a DIY foot pump.

    What I’ve learned over the past year…

    (1) Read everything you can on everything RV, off-grid, boondocking, etc. You can’t learn enough about this stuff, and there are a lot of good ideas out there.

    (2) Don’t scrimp on the important stuff. I’m so tight I squeak, but when it came time to order a power distribution block (fuse box), I turned down the cheap ebay specials and went with the Blue Sea. Why? Don’t wanna burn up in the middle of nowhere. Which leads to…

    (3) When in doubt, go with a size bigger wire. Read up on voltage loss, wire length, amperages & watts & voltages & stuff. Read up on battery banks, amp hours, how much you can run this for how long, all that good stuff. Read up on tilting your panel for greater efficiency, sun hours v. daylight hours, pwm v. mppt controllers. There’s tons to read, and tons to learn.

    (4) When *really* in doubt, ASK. Email some of these companies…they’ll be glad to help. I sent my diagram to 12 Volt Planet for advice, and they said it looked good. Gave me the confidence to go with the program. And there’s no such thing as a stupid question.

    (5) Adapt, adopt, improvise. See a YouTube video that looks interesting, but won’t quite fit your needs? Tweak it. If it doesn’t work, tweak it some more. I was having a time trying to figure out how to fabricate a faucet for my foot pump. Came across a Rain Bird flex pipe swivel joint at Home Depot that looked like it would be perfect. Attached it to my counter top via a 1″ floor flange, then plugged in the 7/16″ OD tubing that runs into one of my water tanks. Oh, YouTube, btw, is where I found directions for my foot pump. Invaluable source of information!

    I’ve babbled on long enough. All you new guys & gals just getting into this, all the luck to you. Read all you can, learn all you can, then hit the road runnin’.

  32. Avatar JB says:

    Hi Bob, is there a roof rack company you recommend to equip roof AC, fan and solar. Ford Transit medium high roof.
    I’m looking at near San Diego.

  33. Avatar ELTEC says:

    What are common mistakes when replacing?

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