Originally Posted by Caduceus
I've got a pair of 55w Hella 500's wired into my truck already, using the stock wiring and relay that come with it.
I'm thinking of adding a second pair of lights. If I do, is it possible to use the existing equipment, replacing only the wire from the battery to the lights (ie, replacing that wire to a 10gauge so that all 4 lights come off 1 wire)? Will I need to change to a different relay? Is it possible to run all 4 off the stock Hella switch, or will I need to replace the wiring on the switch (which is wired to the fuse box under the change drawer, like the method shown in the "how to" sticky)
With 4 lights, I think the minimum wire gauge I'd be comfortable with is 12ga, so your 10ga would work great. Make sure the fuse to the battery has wires of the correct gauge as well, as if you hook 10ga wires to a 18ga inline fuse, you still have the equivalent of 18ga wire, although at least you'll know almost exactly where the failure point will be.
As for the relay and fuse, it really depends what its rated for.
(55Watts * 4lights)/12Volts = 18 Amps. The Hella 500s ship with a 15A fuse, so I'd upgrade that to at least a 20-25Amp. The relay should be ok, as I believe thats rated up to 40Amp.
As for the switch end of the relay (wire to headlight fuse and/or switch and ground), relays use very little power (just enough to power a magnet), so you'll be fine with your existing wire for that. All the wire on the power side (battery and lights) should be the heavier gauge stuff though.
Oh, and dont forget to check your state laws concerning this, as for some reason my state says I can only have 2-4 headlights total. Being switch powered, you'll probably be ok though since they aren't always enabled and should be counted as auxiliary lights.