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How to Wire a Relay for Off-Road LED Lights

We frequently get asked “should I install a relay with the lights?”  The answer is YES! We also suggest adding a fuse.  It is good practise and should not be ignored.

Here are two diagrams showing you how to connect them using a relay.

You will have to adjust the current ratings for the light you are using. In this case the light do not take more than 10A. That is 120W max. If you are installing lights over 100W it is advisable to multiply the required drain by a factor of 1.2 or more. In other words if you are installing a 330W light bar that has a max drain of 27.5A  then you should select  fuse and wiring of over 33A.

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.

Do I Need A Relay?

When you are not using a relay, the control switch needs to be able to handle the full current of the installed lights.  For lower powered lights it is possible to do so, but it is generally good practice to install a switch with an in-line fuse.  When the current increases, this switch needs to be big.  For anything above 30W we recommend installing a relay.  If you do not install a relay and use a switch, you could end up overheating the switch, melting the wires, and reducing the current that is getting to your lights, making them less bright.

How to Wire your Light Using a Relay

The relay will have 4 points on it, marked 30, 87, 85 and 86.  That is kind of cryptic, isn’t it?

The left side is the pin out of the point is sticking out from at the bottom and the the right side is showing a schematic representation of the relay circuitry.

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

30 – is your power source for your light.  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 – connects 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).

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“What if I don’t always want my LED Lights to come on with my high beams or backup lights?”

That is easy to do. Just install a dashboard switch inline with the control line.  When the dashboard switch is off the high beams will not be able to turn on the relay.

Uncertain how to do this yourself?  Have a look at our prewired Relay Wiring Harness for one light with an up to 180W rating.

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