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Wiring Diagram..pretty pretty please

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Hey, after some questions i realised i am not as 'savvy' as i thought i was.

Im after wiring four spots to my roof rack (55w each), spoke to auto elec today and he said i needed two relays so two pairs of lights not one quad..

Therefore does someone have,or can soemone quickly draw a basic diagram for me, 4 spots/2 relays/ one switch....thanks for any help :rolleyes:


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four lights @ 55w each = 220W. 220/12 = 18.3 A which is a bit close for a 20A relay, a 30A relay would be fine though.

Either source a 30A relay, or use two 20A relays.

The wiring remains essential the same, just in duplicate. the two low-current switching wires will just go to the one switch. Diagram to follow.

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If for a roof rack, I don't think it is legal for them to come on with full beam so the double switch route is not truly legal.

I might be wrong but think that is the case.

Lorries get away with it because their high level spots are in front of the front wheels.


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Hey landymanluke, that is great!! Thanks..quick question, i had a 30A relay anyways, then the auto elec advised me to use two.

I have bouight them both now, so should i use the two 30A relays or just stick with one for sake of ease....thanks...Rob :)

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It's up to you, a 30A relay will be up to it, there's no particular reason to use two.

I have two, simply so i can switch inside and outside pairs, as they have different lenses on them. As long as the relay is suitably rated i see no other (simple) reason to use two.

Make sure you use suitable fuses (10A) and the proper sized wiring.

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We've already worked out that the four lights will be drawing 18.3A, so you need a cable capable of 20A plus.

2.5mm^2 is suitable for that current draw, however 4mm^2 will give less voltage drop over the length of the wire and is a better choice.

If using two relays, you could run two 1.5mm^2 wires, or better, two 2.5mm^2 wires, to avoid as much voltage drop.

Remember to run a decent earth back to the battery too.

There's no harm in using bigger cable, there are a lot of downsides to using cable that's too small- higher resistance means dimmer lights, and warm cables.

Given the choice, always go up in cable size, rather than down.

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