I have a few questions about using a wiring harness with halogen H4 bulbs. After installing the wiring harness, Will my DRL be run at 12 volts instead of the 6 volts it runs at from the factory? Is there a way to wire my headlamps so that the highbeam filament of the H4 bulb is on at half power as DRL instead of the low beam? I know some cars like the Acura EL and Honda Odyssey use the high beam filament at half power (H4 bulbs). Thanks in advance.
Probably the easiest solution for you would be to make your own wiring harness, rather than buy a premade one. I've thought it over for a bit and here's what I've come up with (here goes):
*Take note that I'm assuming that your car has positive switching headlights, not ground-switched.*
Access the m/f switch and locate your high and low beam wires. Differentiate the low beam wire from the parking light wire. Also ensure that your high beam wire shows no voltage with the lights off, ignition on. If it does, find the point on the switch that only gets voltage with the high beams on. Now, using diodes, run jumper wires from these wires to your new relays for high and low beam (terminal 86 with 85 to ground). Connect terminal 30 to the positive battery post, be sure to fuse these leads. Run wires from terminal 87 (in parallel) to your new 9003 headlight plugs. Now ground the ground wires on the new headlight plugs. That takes care of the upgraded harness. Now on to the DRL portion:
You don't even need factory DRL's to do this! One option is to use another relay. Connect terminal 30 to constant power (use a fuse), terminal 86 to the accessory wire on the ignition switch, 85 to ground, and 87 to the high beam wires on your new 9003 plugs, in series. This will cut the voltage in half. The big drawback to this is that if one high beam filament breaks, the good one will not light.
A solution to this is to simply wire them in parallel, with a resistor in line with the filament. Measure the resistance of the high beam filament, then locate a couple resistors that match this rating. They'll have to be able to handle a few amps, though. Now if one goes out, the other one can stay lit.
Finally, if you have factory DRL's, you can run a jumper wire from your factory plug high beam wires to your new plug high beam wires. You'll have to use diodes, though, to keep from backfeeding harmful voltage to your DRL module (like when you turn your headlights on)... and the diodes will need to handle a few amps, like the resistors above.
I prefer the first DRL option above the other two for simplicity. Since you should replace bulbs in pairs anyway, losing both at the same time shouldn't be a problem. Keep a spare pair in the glove box.