Wondering about running one wire from the switch to the front then splitting it to go left and right to the headlamps. That any good?

Or do I have to run one wire from the switch to a relay then two wires with fuses to each headlamp?

Also one fuse for left and right side lights or one wire round the lot??

I'm using Sierra switch packs by the way!

No reason why not, same for the rear, one tail, one fog one brake and two for indicators then split.

I think cars split left and right through a fuse box so any issues you only lose one side.

Regards Mark

[Edited on 1/9/06 by mark chandler]

If your headlamps are the typical 65w main beam, your switch will need to be able to cope with 11amps continuous, otherwise a relay would be required.

If you went with the one wire option, and the circuit failed, would you lose both headlights? If so, it's a potential SVA fail

quote:

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Originally posted by StevieB
If you went with the one wire option, and the circuit failed, would you lose both headlights? If so, it's a potential SVA fail

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I was just thinking in terms of the circuit failing and then both lights not working - I thought you had to have separate circuits so that if one fails, you at least have the other working?

You have to have sidelights wired so they can be left on without dip or main headlights so car can be driven on sidelights (something which should be banned IMO) & also without ignition so they can be used as parking lights. Don't think there are any other rules re separating light circuits

My understanding is, that for several years now, if the car is moving anywhere and you need lights on, it HAS to be dip headlights as a minimum, not sidelights.

Headlight must be used when moving - we should rename sidelights as parking lights !
Steve @ sVc
ps
if its getting dark, don't run on sidelights as, if you have an accident, you have signalled that you think that lights were needed by putting on your sidelights, but were not using legal lights, so plod will get you.

Highway Code says:

93: You MUST

use headlights at night, except on restricted roads (those with street lights not more than 185 metres (600 feet) apart and which are generally subject to a speed limit of 30 mph)

I understood that to mean that you don't need to use headlights in built up areas which meet the criteria above.

Back to the original thread....

If you use one wire and then split at the first light, you will need to ensure the main portion of the wire will take the current of BOTH lights.

Worst case is 2x65w, which is a little over 11 Amps. So the normal 8 Amp wire is insufficient.
Personally speaking I would run two sets of wires one for each side, as this is what most modern cars do. Also you can use one piece of 8 Amp wire for each light.
Also make sure the feed to the Relay is big enough for the total load with a little left over for safety factor. (I would use a relay for Main AND Dip beams, ie one for each like the Sierra loom does)

Also the thinner wire is easier to bend round the corners.. especially when you have a few of them.

If you are doing a scratch loom, then draw out each separate circuit that you are doing, and label everything up, or use a strict colour code. Or you will find it a PIG to work on or fault find later on.

Above all Make sure its safe, you don't want hours and hours of your time to go up in smoke do you.

I think he meant running the lights in parrallel rather than in series, as I think you mean. IE splitting just before the first light rather than one light powering the next. Unless I've misunderstood both of you!

Just thinking out loud here....

For my wiring I have put a relay in so that the light switch just goes to ground and closes the relay. I have thick 11A or 17A wire going from the relay to the engine bay where I was going to do as the OP suggested and split it off to the lights.

Now here's the thing. My wire is thick as buggery but the wiring harness that came with the lights is really thin. Now, I would be surprised if the manufacturer sold a product that had inadequate wiring (especially in these compensation culture times) but if that little wire can handle it then where do they get it from as I haven't found anything small like it for 11A or even 8A.

Thinwall wire is much smaller in diameter and therefore takes up less room in the loom. Most older looms will have the thicker stuff but with the same mm2 copper. Most wiring suppliers stock thinwall