Headlamp Relay Harness - Driving Lights Feed

[Daxed 7]

Is it ok to tap into the H4 connected relayed harness and take a supply to the driving lights? Or will this just defeat the whole purpose of the new loom.

 

Relay Harness (thanks to welshpug for the find. Amazing value. Ordered 11/03/18, arrived 19/03/18)

https://www.ebay.co.uk/itm/192284936495?_sp=p2488212.m41214.l9765&_trkparms=itemid%3A192284936495

 

H4 Headlight bulbs - Phillips Racing Vision 150

 

H3 Driving light bulbs - Osram Nightbreaker Unlimited

 

Thanks people who have some idea what Amps are. 

 

[Anthony 1,000]

So you want to run both the driving lights and high beams off the same circuit on the relayed headlight loom?

 

That should be fine, assuming (and that's a big assumption with no names Chinese stuff) that the wiring gauge and fuse was sized to match the 40A relay.

 

Each 55W bulb is going to be drawing around 4.5 amp, so even with four of them you're still only around half the 40A capacity of the relay.  I can't see what size the fuse is or tell what diameter (and hence current carrying capability) the wiring is.

 

If you start running higher wattage bulbs you might run into issues though, particularly if the wiring has been somewhat under-specified.

[Daxed 7]

Thanks Anthony,

 

Fitted fuse is 40 A

 

Wire is 18 AWG

 

Same feed & earth is shared  between high & low beam.

 

 

The calculator doubles the one way cable length to include voltage drop from the earth. The lights will be locally earthed, negating this allowance.

 

So a V drop of about 5%?

 

Workable?

[Anthony 1,000]

18 AWG seems somewhat under-spec to me - I'd have been expecting something more like 14 AWG, especially with a 40A fuse fitted.

 

That volt drop is on the high side which negates part of the benefit of the relayed setup in the first place.  I think I'd be tempted to leave that loom solely for the headlights to get maximum benefit and add a 2nd dedicated feed for the driving lights if required.

[Daxed 7]

Lovely, thanks for the advice Anthony. I will proceed as per.

 

Cheers,

 

Steve