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How to Wire a Relay for Off-Road LED Lights

A common question we get is, "What is the relay for and how do I wire it up?" So here is an overview of what a relay is, why you likely need it, and how to wire it up.

What is a Relay?

A relay is an electrical switch. It allows a low current "switch" circuit to control the electricity flow of a high-current circuit load, like your LED Light bar for example.

Why Do I Need A Relay?

When you create a circuit (a loop of electricity from the battery to your LED Light bar), if you just put a switch between the battery and the light, it will have to be rated for the full current (amp draw) of the light. Our lowest amp draw LED light pod has an amp draw of about 1.4 amps. Many switches would be able to handle that...but if you are using, say our 50" LED Light bar, that has an amp draw of about 17.2 amps, which may be too much for that little switch to handle. As a result, you could end up overheating the switch, melting the wires, and reducing the current that is getting to your lights, making them not as bright.

Check our our selection of LED Light Bars

LED Light Bar

Another reason you may want a relay is for the creative ways you can use electrical currents from things other than a physical switch. Let's say you want have your LED Light Bar come on with your high beams, or reverse lights, for example. Read more about that below. 

How to Wire your LED Light Bar Using a Relay

The relay will have 4 prongs on it, marked 30, 87, 85 and 86. Kind of cryptic isn't it. Well if you are just going to use our wiring harness, and switch, you don't need to know what any of this is, because it comes all pre-wired and plugged in together. 

Buy a Wiring Harness

wiring harness

But if you want to use some sort of electrical current to activate your LED lightbar, like make them come on when you turn your high beams on, or your reverse lights on (if you are adding LED backup lights), then you'll need to do a bit of rework. 

First, let's explain the what these 30, 85, 86, 87 numbers are. Let's start with a picture:


Image of a Relay

30 and 87 create the switch to your LED lights. By default this switch is open, so current cannot get from the battery to your lights.

30 - is your power source for your LED lightbar. It connects to the positive (+) side of your battery or to a switched power source that only gets power when your ignition is on.
87 - goes to the positive side of your LED lights.

85 and 86 use electrical current to create a magnetic force, which then closes the 30 to 87 switch and allows the electricity to flow to your lights. Without this current, no magnetic force is created, so the 30 to 87 switch stays open, and your lights stay off.

85 - connect to the power source that you want controlling the switch. For example you could splice a wire off your high beam wire or off your backup light wire
86 - connect to a ground.

(Note: 85 and 86 can be reversed, but our harnesses have them setup this way).

"What if I don't always want my LED Light to come on with my high beams or backup lights?"

Good question! So you'd want another switch on your dash that you turn off and on. When it is off, and you put your high beams on, your LED light will still be off and vice versa. In this case, you need to wire the dash switch in between the trigger current, i.e. the line you spliced off your high beam wire or your backup light wire. 

With our wiring harness, all you need to do is cut the wire coming from the switch to the 30 prong on the relay, and wire it to your high beam lead or your backup light wire. That way, when you do have your high beams on, the current from that goes to the dash switch first, and if that is off, the electricity can't get to the 85/86 circuit to create the magnetic force to close the 30/87 circuit, which turns on your LED lights.

Still Have Questions?

No problem, we are here to help. Just give us a call on our toll free number at the top of the screen and we'll walk you through it.
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Comments
1/24/2016 3:07 PM
could I connect the reverse wire to 85 as well as to an on off switch so my lights come on during reverse and while parked just flip a switch and lights will come on that way as well.
2/5/2016 6:16 AM
@nathan:

Yes, you can do this; basically, you would put your switch in between the reverse wire and 85, so that the relay would only trigger when the switch was on (to make the connection to 85).

You could even do this: Get an SPDT switch, with center off, and wire the common terminal (center, usually - but check it first) to the relay (85). Now, wire one of the remaining switch terminals to your power source, and the other to your reverse wire.

Now, when you set the switch to the middle (off) position, your reverse lights operate as normal (and don't trigger your extra lighting). When you flip the switch one way, your reverse lights will operate the relay (and your light setup). When you flip the switch the other way, your lights will turn on independent of the reverse lights.

This is a simple modification that might be worth doing depending on your needs, because after all - who wants to redo their wiring if they don't have to, right?
4/18/2016 5:48 PM
can I run my 35 inch led light bar of my 2015 gmc sierra driving light switch if I use a relay? thanks
8/23/2016 4:23 PM
I have a relay kit with a switch already, I want my led bar to turn on with the high light switch. Can I just connect the wires that go to the battery to where the high light, and keep custom switch on at all time?
8/23/2016 5:21 PM
@frank, no you wouldn't want to do that as the LED light would then try to draw all the power to run it from the same wires/circuit that is powering your high beam lights. That circuit isn't meant for that additional load and would likely blow your fuse.

Instead, you'd need to splice a wire from your high beam wire to the 30 prong on the relay. Then if either the high beams come on OR you flip the switch, either one of those will close the relay and turn on the LED light.

Hope that helps!  
10/11/2016 8:46 AM
I have followed this helpful instruction here to a "T"..
But only half of each aux rear lights light up.. each light has 6 LED's but only 3 on each are lighting up..
can anyone advise..
2/15/2017 8:45 AM
I have a light bar that came with a wiring harness and switch. I want to remove the factory switch as i am running multiple light bars and use a third party switch panel with 6 rocker switches run in a series.  On the back of the rocker switch, there are 5 blades.  Two ground, two hot and a 5th blade that goes to the Relay or LED.  These are 20 amp switches.  My question is, the switch panel needs to be run to positive (accessory or ignition) and the remaining open blade will run to the wiring harness.  But in the wiring harness that originally came with it, there are three wires going to the factory switch..Red, black and yellow that lead back to the relay.  I am assuming the remaining open blade will correspond to the yellow wire in the wiring harness.  But, what I am to do with the red and black wires in the wiring harness?
3/23/2017 7:57 AM
I wired my 50" led light bar up with the wiring harness supplied with and the switch also, but the red light on the switch stays on when off position it lights up green when on . My question is should the red light ALWAYS be on even with key in off position? Thanks
10/11/2017 9:23 PM
Thanks mate, helped me no end, identified faulty relay. light bar working again. I live in the Australian bush and we work on the principle when driving at night, "the more light the better".
11/4/2017 3:01 AM
Isn't this illegal? Light bars need to be wired into high beam