How to Wire a Light Bar Without AUX Switches (3 Ways)

Bolting a light bar onto your truck is the easy part. Getting power to it is where most DIY installs stall, especially if your truck doesn't have factory AUX switches. The good news: you have three solid options, and none of them requires you to be an electrician. Here's how each one works, what it costs you in time, and which one we'd pick.

Quick answer

If your truck has no AUX switches, you can wire a light bar three ways: (1) a wireless switch harness that mounts in the engine bay and runs from a remote in the cab, with no wires through the firewall; (2) a generic relay harness with a switch, which means running one wire through the firewall to the dash; or (3) tying the bar into your high beams with a relay. For most DIYers, the wireless harness is the fastest and cleanest.

First, check whether you actually have AUX switches

A lot of newer trucks ship with factory AUX (upfitter) switches and don't advertise it. Look for a row of numbered AUX buttons on the dash or overhead console. Many Ford trucks (Super Duty, F-150, Ranger, Bronco), many RAM trims and some Toyota models have them, depending on trim and package. If you do, use them: the light bar wires straight into the AUX leads in the engine bay and you're done. Our guide on why AUX switches are a game changer covers how that works.

What's coming out of the light bar

Before picking a method, know what you're connecting. On our light bars:

PRO light bars have 3 wires: red = main white or yellow light, black = ground (to the chassis), white = amber DRL. The lead is 8+ ft long and ends in yellow crimp connectors.
SLIM light bars have 3 wires on the dual-function version (red main, black ground, white amber DRL) and 2 wires (red and black) on single-color versions. The lead is 6+ ft long.
Ditch light kits ship with a harness that joins both pods and runs one power lead.

Black always goes to chassis ground. Red (and white, if you have a DRL) are the positives that need a switched power source.

M&R light bar wiring connection guide — red main beam wire, black chassis ground, and white amber DRL wire

Option 1: Wireless switch harness (no firewall wiring)

A wireless harness puts a fused control box in the engine bay, wired to the battery. Your light bar plugs into one of its circuits. In the cab, a battery-powered remote with a magnetic mount turns each circuit on and off. Nothing runs through the firewall.

M&R wireless switch harness wired to the battery in a truck engine bay, bolted on with no wires run through the firewall

Time: usually under an hour
Skill: connect to the battery, crimp a few wires
Bonus: 8 circuits, so the ditch lights, fogs, reverse lights or a compressor can go on the same system later

Our Wireless 8-Switch Harness 2.0 is rated for 100 amps total and adds low-voltage and sleep protection so it won't drain your battery. Full breakdown: the wireless switch harness, explained.

Option 2: Generic relay harness with a dash switch

This is the classic method. A harness with an inline fuse and relay connects to the battery, and a thin switch wire runs through a firewall grommet to a rocker switch you mount in the cab.

Time: 1 to 3 hours, mostly finding a path through the firewall
Skill: moderate; you'll pull trim and fish a wire
Watch out for: a cheap harness with thin wire or a weak relay. Match the harness rating to your light's amp draw.

For a dual-function bar (main + DRL), you'll need two switched circuits, or a dual harness, if you want to control them separately.

Option 3: Tie into the high beams

Some people trigger a relay off the high-beam circuit so the bar comes on with the brights. It works, but on newer trucks the lighting circuits are computer-monitored, and tapping them can throw warnings. We don't recommend it unless you know your truck's wiring well.

Which one should you choose?

You have AUX switches: use them.
No AUX switches, want it clean and fast: wireless harness.
No AUX switches, want a physical switch on the dash and don't mind the firewall: relay harness.
Planning more lights later: wireless harness, because you'll already have 8 circuits ready.

Safety basics, whichever way you go

Fuse every positive lead close to the battery.
Ground to clean bare metal on the chassis.
Seal crimp connections with heat shrink and keep wires away from heat and moving parts.
Main beams are for off-road use only. The amber DRL is a low-glare accent light.

FAQ

Can I wire a light bar without AUX switches?
Yes. Use a wireless switch harness, a relay harness with a dash switch, or a relay off the high beams. The wireless harness avoids running any wire through the firewall.

Do I need a relay for an LED light bar?
Yes, unless you're connecting to factory AUX switches or a switch harness that already has relays and fuses built in.

Where does the black wire go?
To chassis ground, on clean bare metal. Not to an AUX lead.

Do M&R light bars come with a wiring harness?
Light bars don't; the attached lead is long enough to reach factory AUX wiring. Ditch light kits include a harness that joins both pods.

Will a wireless harness drain my battery?
The 2.0 version has sleep mode and low-voltage cutoffs that shut everything down before the battery gets too low to start the truck.