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: https://cheaprvliving.com/blog/how-to-install-a-cigarette-lighter-plug-strip-and-crimp-12-volt-wire/ 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 Amazon.com 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.)
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.
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:
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: http://circuitwizard.bluesea.com/#for 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:
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.
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.
Step 3: Strip and crimp a ring connector to the black (negative) wire.
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 Amazon.com: In-line ATO/ATC Fuse Holder 16 AWG
Step 5: Wrap all the connections you just made 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.
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.