How to Wire a Light Bar

Now that you’ve installed your new LED light bar to the vehicle, it’s time to connect it with the power so you can light up the night landscapes. Wiring an LED light bar correctly ensures you have a safe and reliable experience.

1. Disconnect from the Power Source

This is always the first step in any electrical work. The battery in a car or truck can seem pretty harmless, but if you’ve seen one spark before you’ll appreciate that it can deliver a painful or even lethal jolt of electricity.

Before you do anything else, disconnect the negative battery cable (usually black) from the battery. This grounds to the entire vehicle, so if it’s in place you could still get shocked by the positive cable if it touches any part of the vehicle. To be extra save, make sure the loose clamp is in a place where it won’t spring back toward the terminal. When the negative cable is disconnected, you can safely disconnect the positive (usually red) cable.

2. Sizing Your Wire

Wire must properly sized to the current because wire that’s too thin will overheat, causing it to melt the insulation and possibly start a fire. Wire comes in different gauges, or thicknesses. Since your vehicle runs on 12VDC, you can probably use standard automotive wiring, but check your specs to be sure what kind of wire is recommended for the light bar.

If your manual doesn’t have that information, you will have to determine the right gauge and length of wire that is equal to or greater than the product’s maximum current (amp or ampere) draw. You can find a chart here.

To be safe you could go one size larger.

3. Wire Grades

There are also different quality grades. Standard automotive wire is GPT wire. But there are higher grades called GXL and TXL. These are more heat and chemical-resistant. If you find them and have the extra cash, get them, but GPT will probably do fine.

4. Wire Connectors

If your manual doesn’t give suggestions on electrical connectors, you probably need an IP67 or somewhat higher rating. Connectors should be watertight for all kinds of off-road conditions. You may be able to find them in the boating section if not the auto section of the supply store. Watertight connectors fir snugly and don’t require any electrical grease or tape. Use a pair of wire crimpers that are specified for the connector you choose. If you feel it’s necessary, use a marine-grade product.

Wrap electrical tape tightly but don’t stretch it, or it will start to loosen quickly.

5. Relays

If your light bar draws more than 5 amps, you should use a relay to be safe. A relay or switch can protect your light bar if something goes wrong and the vehicle electric system overloads. A fuse number doesn’t correspond to the wire size but to the expected current. A 40A automotive relay should be plenty, but check your specs. Just be sure the relay capacity exceeds the light bar’s maximum current draw.


Relays use a cab switch carrying 1A or less. So you can use a much smaller cab switch and switch circuit wire than the wire supplying power. However, use at least a 10A switch. Connect relays and switches into the positive wire.

If a wiring harness with a built-in relay came as part of your LED light bar package, you should stick with that.

6. Wire Routing

Route your wires along the firewalls and vehicle chassis. Try to keep the length no longer than necessary. Keep them away from the engine and other heat sources. Avoid splicing wire if you can; you might want to buy a little extra in case of errors. If you have the LED light bar installed on the roof, try to run the wire through a window channel. It might also be a good idea to add a separate connector near the light bar so you can easily remove detach it if necessary.

To keep wiring easy to trace for you or the next vehicle owner, use different colored wire for each purpose, typically red wire for power, black for grounds, and yellow for switches.

A lot more detail could go into wiring, but with this information you should be able to run power and install any desired relays to have your LED light bar connected and powered safely. Absolutely take into account any wiring recommendations and specifications given in installation instructions coming with the light bar. If you have any doubt, or run into problems, ask an electrician. Just be sure you disconnect the battery before doing any electrical work on the vehicle.