so, i got my new H4 headlights with the 55/100 bulbs. i also got 4 good relays to make sure the headlights get all the juice they need.

here's my question:

- shouldn't i be able to just run 1 (one) heavy gauge wire to each side?

i might be thinking this through too much, but i never use the low beams and high beams at the same time, so why not share the 12V feed for both (per side) ???


does that make sense at all?
Andy

I'll let others speak to the details of wiring the relays in such circumstances, but I would think you're onto something.

You can run just one wire up to the relays, if you like. Just make sure it's big enough to carry the maximum current you expect to draw over the distance of the wire run. Make sure to put a fuse in-line somewhere near the battery, too.

Oh, and remember--most electrical things take more current to start going than their steady-state draw.

--DD

Thats a good point for something like a set of HID headlights where there is a large differential between steady state and startup condition, but for an incandescent headlamp the difference isn't much and the startup condition is much shorter.

If an incandescent bulb reaches steady state in a millisecond or 10, the wire isn't going to measurably heat up. For an HID light it takes up to several seconds.

One wire sounds good Andy, but be careful about stranding multiple smaller wires. Bundled wires don't add perfectly. For instance 10 wires capable of handling 1 amp each, bundled together cannot handle 10 amps total.

-Tony

Yep, I just sent one big 'ol (fused) ten guage up to the front for lights and one for audio.

andy....

you could probably get away with 1 relay for low, and one for high...


BTW - where are you mounting the relays?

I ran 1 10 gage wire from the battery to the front trunk, installed a fuse panel at each end, then 2 relays, 1 for low, 1 for high. Before I did that I had a 2 volt drop between the battery and the headlights, now it's .2 volts. Lots more light from those halogens now. Also ran a couple of extra wires while I was at it, never know when you might want to install something else, CD player, etc.

Good Luck, Don

OK, here's a question. If you just use two relays, one for low beams and one for high beams, do you run the wire from just one side from the switch, or do you splice the 12V from each side together to energize the relays? Obviously power out to the lights will be two wires coming out from the relay. So, one wire, or the two spliced(driver and passenger) together to energize the relays? Does that make sense? A schematic would be nice.

Here's some good info...

Here is another good source for headlight relay information:

http://www.danielsternlighting.com/tech/relays/relays.html

It seems you could use the output from the hi/low relay to power the new relay coils, then run the new power through the new relay contact to fuses to the lights (similar to stock, one fuse per light). This is basically the second diagram from Daniel Stern's site

Damn! That's SMART!!! I've definitely filed that away for future projects.