Auxiliary Light Wiring Guide

Possibly the most popular, and one of the most practical accessories for any off road or overland vehicle is auxiliary lighting, whether this be spot lights, work lights, rock lights, beacons…etc. We’ve seen many many people on various forums and out and about who find installing auxiliary lighting confusing, so this short guide will hopefully help!
Auxiliary lighting basics:
Auxiliary lights usually range in power draw from the standard 55w incandescent bulb upto 100w. There are other variants such as HID systems (bit more complex, we won’t go into them here!), LED, and other systems such as the X-Eng systems that we recommend that use a 50W halogen bulb.
You then have different beam patterns suitable for the lights intended use, such as flood pattern for fog and work lamps, and several different throw patterns of spot lights.
Wiring basics:
We will be explaining 12v vehicle systems, although there is little difference between 12v and 24v systems, and the majority of you will have 12v systems.

Diagram 1 - General Auxiliary Light Wiring

In order to power an auxiliary light, you will want to connect the light to a power source, and in most cases a switch. The safest way of doing this is with the use of a standard 12v relay. The diagram above shows how a relay works, you connect a suitably high current positive (+) wire from the vehicles battery, with a suitable fuse to protect the light and the battery, if you are installing lots of accessories then its easier to use something like a 6-way or 12-way accessory fuse panel to label and organise different circuits. The relay must then be earthed to the vehicles chassis somewhere. The last input the relay needs is a switched positive source, this is where you can start to get imaginative with how your circuits work, we will go into this in more depth later in the article, but for now lets just say that this is connected to a new toggle switch on your dash which in turn is connected to your battery (we usually tap into the vehicles cigarette lighter or high beam light feed…etc, depending on what we are doing), this is just a switching connection so won’t draw very much current….this isn’t powering your lights.
The last connection on the relay is the 12v output which will power your lighting circuit, we don’t recommend connecting more than 2 lights to one relay unless they are quite low power lights, you can wire more than one relay side by side and just split the switching cable into both.
So on your auxiliary light you will have the 12v positive input (usually white on the light itself) and an earth (black wire) which you connect anywhere with a nice clean connection on the chassis.
What happens now is the relay is always powered, and when you throw the switch a small 12v current is sent to the relay which throws a contact, connecting the auxiliary circuit to the battery or fuseboard etc…and with any luck you will have light. If you haven’t the most common problem is a poor earth.
More Advanced setups:
Despite calling these advanced setups, they aren’t really difficult or confusing, they are just a bit more thought out and purposeful then flicking a switch!
Lets start with spot lights, do you want them to come on with your high beam, dipped beam, do you want them to turn off when you take your keys out the ignition?…etc. All of these are simple enough, you just connect the switched input on the relay to something in the relevant circuit, you can also put a switch inbetween so that your spots will come on with your high beams…but only if the switch is on also.
The same goes with work lights, do you have a work light on the rear? If so you probably want it there in order to make reversing in the dark easier, so why not connect the switched input to your reverse light circuit, again you can have a switch on your dash that this goes through so that when in driving on the road you have the option of not having it come on when you throw the vehicle in reverse.
So now we have circuits that are more tailored to our needs which is great, but lets think about the reverse light that we just setup, so you are on dark trails and you have your rear worklamp on to prevent smacking trees when you are reversing out of a trail or something on the way to your stopover point for the night. When you get to the stopover point, you need to cook dinner or setup your tent…etc, and could do with some light to help you. In order to turn your light on you need to stick the vehicle in reverse with the dash switch on, not ideal if you forget and start the vehicle and run over your dinner….or tent….or girlfriend…etc! What we can do is stick a more advanced switch on our dash in place of the on off one we had earlier, lets say an ON-OFF-ON switch, this type of switch has two inputs and one output, so keep the output to the relay, and one of the inputs from the reverse light circuit, but then connect the other input to something that is always on, like your battery or in some cases the cigarette lighter …etc. Now you have the option of switching your worklamp OFF altogether, ON when you throw it in reverse, or ON all the time regardless, as in Diagram 2 below:

Diagram 2 - Auxiliary Light Wiring with On-Off-On switch

 Now go wire s**t up!!

3 replies on “Auxiliary Light Wiring Guide

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  • Andy

    Thanks very much for such a simple and straight forward guide. I used ‘Diagram 2′ for both my work/reverse lights and then again for my main/lightbar lights. I’d have done ’em sooner if I’d have realised it was so easy!

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