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HomeTips & GuidesHow To Attach LED Light Bar Wire Harnesses To Car Battery: 7 Installation Steps To Follow

How To Attach LED Light Bar Wire Harnesses To Car Battery: 7 Installation Steps To Follow

Here’s how to attach LED light bar wire harnesses to car battery.

The conventional vehicle headlights are enough for regular driving conditions. 

But offroaders like to mount LED light bars on the roof, bullbar, or front grill of their trucks and SUVs for safer nighttime driving. 

Driving offroad around tight corners and on narrow roads requires excellent visibility, which headlights cannot provide. 

So, LED light bars are necessary for such car owners. Read on to learn more.

Table of Contents

Required Tools and Materials

You need the following items to complete this installation.

  • LED light bar
  • Relay
  • Fuse
  • Wire harness
  • Drill
  • Socket set

How To Attach an LED Light Bar Wire Harness to Your Car’s Battery

Follow the steps below to get the job done.

Step 1: Mount the Light Bar

Pick a location to mount the light bar, which should be a sturdy spot on your vehicle that can project the light beam ahead. 

Some suggestions include the bullbar, roof rack/cage, and front bumper. Consider your local area laws when picking the mounting location.

When roof-mounting the light bar, you might have to drill holes through the vehicle to attach the brackets that come with the light bar. 

Although you will seal the holes after drilling, this procedure might leave tiny pores that leak water during heavy downpours. 

And if you’re like me, you wouldn’t want to damage your vehicle’s body.

A convertible vintage truck with an LED light bar mounted at the top for offroad driving

A convertible vintage truck with an LED light bar mounted at the top for offroad driving

So, the next best alternative is to use tube clamp brackets to mount the bar to your vehicle’s OEM roof rack. 

But if your car does not have roof racks, you’ll have to drill mounting holes.

The other mounting locations are easier to implement, especially the bullbar.

Step 2: Disconnect the Battery Negative Terminal

Disconnect the negative wire from the battery’s negative terminal to avoid shorting or grounding electrical faults. 

You can attach a memory minder to your vehicle’s 12V accessories, such as the head unit and clock, to avoid resetting the time or losing saved stations.

Step 3: Mount the Relay and Fuse

Although LEDs have a lower power draw than regular headlights, we recommend using a relay over a simple manual switch to protect the switching operation.

Relays are electromagnetic switches that use low-current control circuits to operate high-current circuits. 

They eliminate direct contact between the handle and the light bar, making the system safer.

An SUV rigged for extreme offroading with an LED lightbar on the roof

An SUV rigged for extreme offroading with an LED lightbar on the roof

A fuse is also necessary for the circuit to protect the LEDs, relays, and wiring harness from destructive electrical faults, such as power surges.

 The fuse will sacrifice itself, creating a discontinuity in the power flow before damage hits. 

It is a cheap component; replacing it will be more pocket-friendly than replacing a burned relay or light bar.

Identify suitable locations for mounting these components in the engine bay, close to the battery, with the fuse sitting between the battery and relay. 

Remember to install a fuse that matches the light bar’s power draw.

Step 4: Connect the Light Bar Wiring Harness to the High Beam Headlight Circuit

Instead of using an auxiliary switch to activate the light bar, we recommend using the existing car’s headlight circuit to power the relay to switch on the LEDs.

This option also has another benefit. It will prevent you from leaving the LED light bar on when you switch off the vehicle and turn off the headlights. 

So you won’t accidentally drain your battery.

Find the high-beam headlight globe nearest the relay and unplug its adapter. 

Pick the headlight adapter in your light bar kit that matches this plug and attach it to the power plug. 

Connect the secondary plug to the headlight bulb and the third adapter to the light bar harness.

An offroader with its two lightbars and headlight high beam lights on

An offroader with its two lightbars and headlight high beam lights on

Step 5: Mount the Master Control Switch

Picture this scenario. You are driving on the highway and put the high-beam lights on. 

The light bar also turns on, but you don’t need it. You need a master switch for this control to turn it off. Mount it at a convenient location near the driver.

Step 6: Run the Switch Wires Through the Firewall

Run the wires from the fuse and relay in the engine bay through the firewall to the switch in the cabin. 

Instead of cutting or drilling a hole into the engine bay, try to find an unused grommet and channel the wires through this path.

But ensure the cable has a drip loop to keep water from leaking into the cabin. We recommend using sealant around the hole to plug any pores.

Lastly, connect the light bar to this wire harness by linking its power supply line to the relay and ring terminal to earth (contact the vehicle’s body or negative battery terminal).

Step 7: Reconnect the Power Supply

Reattach the negative battery terminal lug to the post and tighten it. Test the light bar by putting the master switch on, then turning on your headlights to full beam. 

Also, check if you can switch the light bar off when the high beam is on by turning off the master switch. If all the tests are successful, you are good to go.

FAQs

Here are answers to the most frequently asked questions about LED light bar installation.

How To Attach LED Light Bar Wire Harnesses To Car Battery: Can I Wire an LED Light Bar Without a Relay?

Yes, you can. But not all light bars. LEDs generally consume little electrical current, and relays eliminate high-current switching from the manual switch you operate by hand. 

So, if LEDs consume little electrical current, there is no need to have a control circuit.

But light bars have multiple LEDs, which can add up the power draw to a significant figure. 

So, it is safer to use a relay, especially if you don’t understand amperage ratings and measurements.

An offroad sport truck with a roof-mounted LED light bar

An offroad sport truck with a roof-mounted LED light bar

How To Attach LED Light Bar Wire Harnesses To Car Battery: How Can I Hide Roof Rack Light Bar Wires When Running Down From the Windshield?

Use any of these four options.

  • Drill a hole through the roof and run the wires inside the A-pillar to the firewall, then into the engine bay, or directly into the engine bay. Seal the hole carefully when using this option to prevent water leaks into the cabin.
  • Use a wire or cord hider to conceal the wires as they run down the windshield next to one of the A-pillars.
  • Mount the wire harness in the windshield weather stripping, then run them to the engine bay.
  • Insert the wires in a loom, then run them down the windshield pillar to the relay in the engine bay.

Wrap Up

Dealing with a vehicle’s electrical system is tricky, so be careful when handling your light bar installation. 

But in general, the process is straightforward. After mounting the fuse, relay, master switch, and light bar, you only have to run the wires neatly in the vehicle and make precise connections. 

That’s it for now. Check out our car headlight relay article to learn about vehicle light switches.

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

Contact me now and let’s get started on building your wire harnesses!

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