I don't want to pick fights here, but ...
it'll light the full beam filament in the main headlight as well, as in the spot.
The purpose of the diode is to not light both bulbs simultaneously, otherwise a bridge wire would suffice, the diode is there to prevent reverse current flow.
looking at your diagram it appears that the dioed is going from the wire shown as brown whitch i would presume is dip headlight to wire shown as yellow whicth i presumed to be main beam, if it the other way round it will work as desired but i still don't like that dioed, it's costing you .6volts and it dosent even need to be there, it choudl be replaced by a pair of 0.5A dioeds on the relay. bridge brown 86 to yellow 86 with dioed, then put another iin the yellow wire going to the relay, sorted cheepr and more voltas at lights
also haveing spot lights on with dip beam will piss other road users off but full beam as will is really takeing the piss.
The spots on a my Golf point down on the road - they are not for distance.
thats not going to piss other road user off then, but a lot of thingys wouldn't think to do that
just as well that dioed will pop really quickly it'll be trying to handel roughly 14 amps the biggest commonly avalible black dioed is 3A
RS (the comp. shop I use mostly) sell about 3000 varients of diode that can sustain 50A+.
i use them to, my point was that the 3A dioed was the biggest common dioed yes MUCH bigger ones are avalible but they get expensive, i much prefer to use 2 tiny ones to make the relays do it right. it's eating 10 watts your headlights chould have had
as for cabel size 100w x 4 = 400w. 400w @ 14.4 v = 27A id go for 2.5mm2 to carry the power. and .75 will be more than enough to throw the relays
The +ve lead isn't running all four lamps, its two +ve cables from the batt, so 200W max. Which is about 17/18 AWG, about 1.1 mm2.
depends how you make loom, if making a left and right 1.1 would do tho you'd end up useing 1.5 as it's common, but if making it as one whitch i'd proably do one 2.5 off the battery into one pair of relays and off to the other pair would also be fine. i would also add another wire to the diagram, a 2.5 0V line from the headlight bulbs back to the battery not really that inportant but car bodies arn't that good at conducting.
