Anyone tried this yet, to improve light output from OEM low beams?

I recently installled some low $$ Hella driving lights, with 55 watt halogen bulbs, switched via relay, with 12 gauge service throughout, and the brightness is far in excess of the OEM 55 watt halogen bulbs. The wiring for the stock lowbeams looks like 20 gauge...pretty skimpy stuff for pulling 4-5 amps.

I've looked at the Subaru manual, and I'm semi-stumped on working a relay control for the + feed/how to run a shorter, more direct ground, with the involvement of the daytime running light module/DRL relay, etc...possibly some use of diodes? Ideas?

This is on a MY04 WRX, tho I suspect the circuitry is essentially similiar to previous years, with the exception of bulb type.

I wouldn't bother with the positive. Almost all the loss/voltage drop in the headlight circuit is on the ground side, due to the switched grounding circuitry. The positive side, aside from the narrow gauge wiring, isn't that bad because there is a separate power feed for each side that uses a relay, and the wire path is shorter since it's all in the engine compartment.
Adding a relay controlled by the low beam switched ground to provide a direct chassis ground for the low beam will eliminate most of the loss and produce a noticeable improvement in light output. This will also negate the low-intensity function of the DRLs (they will still operate but the low beams will run at full brightness), so you might as well disable them unless you want to drive around with your full low beams on all the time.

Yep, I initially planned it that way, till I looked at the DRL complications...and I'd like to keep that functionality. I have gone as far as running 12 gauge up to the grounded lug on the DRL relay, and connecting that to the ground point on the block under the intercooler....*seemed* to brighten things up, slightly. I ran this added line parallel to the existing skimpy ground line, never could determine where that line actually grounds!

Scrapping the DRL functionality would greatly simplify the process, tho, I agree.

so how much of a difference is there in light output after installing a relay with the stock halogens?

the stock halogens already use a relay... one for each light (look in the underhood fuse box)

Improving the ground could help if the current ground wasn't good (i.e., higher resistance path to ground than would be optimal) - if you want to improve that and have as low a resistance path as possible, just run the ground wire for the lights directly to the negative terminal on the battery with a heavy gauge wire.

i have aftermarket orciari headlights on my 04 and i just measured my positive voltage and the difference was 1.0 volt. i'm gonna wire a relay soon- after this blizzard in philadelphia passes tomorrow.

a question though... do the wrx headlights switch on the negative or positive? according to the daniel stern website, you have to wire it differently depending...

How did you make that measurement? Did you check the drop on the ground side as well, it will probably be more than you saw on the positive side. The Subaru lights use switched ground/common positive.

i have aftermarket orciari headlights on my 04 and i just measured my positive voltage and the difference was 1.0 volt. i'm gonna wire a relay soon- after this blizzard in philadelphia passes tomorrow.

a question though... do the wrx headlights switch on the negative or positive? according to the daniel stern website, you have to wire it differently depending...


A 1 volt drop would make for a significant dimming!

The low beams are controlled by the normal switching arrangement, plus their final leg to ground is switched between the DRL resistor/straight shot to chassis by the DRL relay.

If you're willing to sacrifice DRLs, it's pretty straightforward...I'd like to run heavier wire AND keep the DRLs, that's definitely not straightforward :lol:

if you want to improve that and have as low a resistance path as possible, just run the ground wire for the lights directly to the negative terminal on the battery with a heavy gauge wire.

You'll have full-on low beam operation with that, 24/7, as long as your running with parking brake down...you'd have simply bypassed your DRL resistor. Note also, the + wiring is skimpy 20 gauge crap too...it's not just on the ground side.

i measured using a voltmeter according to daniel stern's writeup- i think it was red lead to battery positive and black lead to bulb positive. the negative measurement came up way too high to be right... but maybe it was? i'll take before and after pics- with and without the relay. btw, i disabled my DRL's so that's not an issue.

so wiring experts- do i hook up the bulb ground to the relay or to the chassis (or battery negative)?

so wiring experts- do i hook up the bulb ground to the relay or to the chassis (or battery negative)?

If you're running it completely off a new relay, use the relay to interrupt + supply to bulb. Ground side of bulb would run straight to chassis. To be sure you're not dropping any voltage due to skimpy wire gauge, I'd suggest 12 gauge wiring service for the + supply, to the relay, and to bulb, and again 12 gauge, from bulb to ground. I'd even attempt to get rid of the short run of skimpy wiring that exists on the headlight assy itself. You can use the original switching circuit for relay control. As you stated, you've done away with the DRL stuff, so this would work in your case.

it all makes sense to me. thanks a ton.