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· Registered
1,608 Posts
Discussion Starter · #1 · (Edited)
Light wiring discussion

Basically, I wanted to start a thread for the DIY enthusiast looking to wire up some applications on his or her Jeep (or whatever it may be). This forum doesn't have one of these where the information is piled into one thread, so lets get the ball rolling.

Lets start with some basic terminology (not everyone knows this stuff right off the bat, or some might be a bit foggy, but that's perfectly okay, we all had to start somewhere):


-A Fuse is a small device, normally made from plastic (older vehicles often use small glass tubes with contacts on each size), that contains a small thin piece of wire that is designed to break (or melt) in the event the current from an electrical circuit flow exceeds a safe level.

You pretty much always want to run some sort of fuse in your Positive lead that runs to your power application, be it some auxiliary lights, a stereo, maybe a CB radio, etc. Running a fuse not only prevents your components from being seriously damaged, but it also prevents your vehicle and its electrical system from receiving damage.


-A Relay is basically an electronically activated switch. Relays can take power directly from your power source (in our case, the battery) and transmit it directly down your power wires to the device you are trying to turn on, using a simple voltage signal from a power switch. Relays are a very safe method of powering high powered components (such as 100 watt spotlights) because the current does not flow through the power switch. Instead, it flows directly through the relay to the component.

Often times, manufacturers include shoddy wiring that inhibits our lights from receiving full power and the required current they need to be driven at max power. Installing your own relay harness (one for high beams, one for low beams) solves the manufacture wiring harness issue, and allows maximum light output which can greatly increase your visibility. Some tests have shown that an increase of 200-300 lumens was received, which is almost a night and day difference.

Fuse Box:

-A Fuse Box is typically a small enclosure that contains all of your systems fuses for your lights, radio, and other misc. components you may have installed. Fuse Boxes create a very clean, very organized layout in your vehicle that keeps all of your fuses in one location. It makes finding a blown fuse VERY easy, so that you don't have to hunt it down if you have wires running everywhere. Some fuse boxes also have room for relays, so that you don't have to install relays externally. Typically Fuse Boxes connect to your batteries Positive lead to make wiring even easier.

Here are a few wiring diagrams to give a visual aid on how to wire up your components properly.

This is typically the best way to wire up your aftermarket lighting (if they don't include a wiring harness) using both a fuse and a relay:

This diagram basically shows the layout for making your own relay and fused wiring harness for upgrading the wiring for your headlights:

And this is a fantastic diagram of how to wire up multiple relays using a fuse box to activate multiple applications of your choice:

If you have any valuable content to add to this thread, please feel free to post it, and I'll do my best to add it!!!

· Internet Owner
9,494 Posts
Good info! Thanks for posting it.

· Registered
858 Posts
I cannot believe I missed this thread of all threads being the automotive electrical/wiring/circuitry nut I am, lol.

Great thread Xpress!

I'll shed some light on 12V DC automotive circuit breakers here very soon to help ya out ;)
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