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Wiring Jeep Lights - Randy's Electrical Corner

Wire for Lights

RandyPhotographer, Writer

Hey everyone, it's me Randy again. This month, I wanted to follow up on last month's "Light Wiring" column. I amgoing to try to explain how to choose what size wire you need to use for whatever it is you are wiring up.

wire size (AWG) 18 16 14 12 10 8 6 4 2 1 1/0 2/0 3/0 4/0
Nominal OD 7⁄64" 1⁄8" 9⁄64" 5⁄32" 7⁄32" 5⁄16" 11⁄32" 13⁄32" 15⁄32" 17⁄32" 9⁄16" 5⁄8" 11⁄16" 13⁄16"
Max Amps 10 12 17 22 30 40 60 {{{80}}} 105 122 142 165 192 222

Using this chart, if we take our 100 watt bulb from last month (editor's note: 6.8A draw), we can see that an 18-gauge wire should workjust fine. But if we are putting in two lights... then we need more like a 14 gauge wire to feed it.

That is my own chart I keep in my brother's El Camino, just in case. I figured that out the hard way, making my way through a lot of melted wires. It is overkill if you look at a real electrical book, but I've found that, in the real world for continuous usage, those numbers work well.

In a Jeep or a car, the wires almost always run through the engine compartment, which makes them hot-which, in the end, means that they carry less amps before melting.

For our 100 watt light from last month, with a proper relay, this is how I'd wire it, with thegauge of wire needed. If the wire goes through the engine compartment, or a long lengthof wire is needed, go to the next-biggest wire in the chart (in parentheses on the drawing).And, even though this drawing shows the wire size changing when it goes to the lights...you could do it that way... I never do. I'd run the big wire even when it splits to go to thelights. I just wanted to say you could do that.

Also, not all wires are created equal. I said that before. But this time, I want to talk about SAE and AWG ratings. That chart shows AWG wire ratings. SAE wires are smaller in diameter and carry less current before they melt because of it. If you aren't sure what kind of wire you are using, you can measure it and see. If it is about 10 percent smaller than what my chart says, it is SAE wire and carries about 10 percent less current.