I'm not the first, and certainly not the last, but I'm pretty disappointed with the lighting on my '95 Impreza. I was considering installing driving lights in place of my fog lights, but I found that I could get a pair of Hella 100w/80w H4/9003 bulbs for $23 through work.

A quick search yielded little information about people running these, though the one case I found listed upgraded wiring and the use of relays. Before I get to into this, is an upgraded harness completely necessary? Worst case scenario, I should be looking at ~7amps per bulb, and each headlight (left/right) has it's own separate fuse. If I remember correctly, the fuse is a 10 or a 15 amp. The stock wiring to the bulbs is fairly small (18ga?), and my drivers side connector is slightly burned with use of stock bulbs. Could I get away with just cutting the plug off and soldering in new female spades, or is the stock harness insufficient?

I pulled up a diagram from alldata, and using that, we considered running 12ga wire to the center prong on the bulb (3 on the diagrams), and using separate relays for the high and low beams. "15a" is the fuse suggestion.



http://img502.imageshack.us/img502/993/headlight1sx1.jpg



It all looked pretty good until we traced the power supply routing in the fuse box. In order to be able to use the stock headlight switch, I would have to use the main headlight relay (MB5 on the Alldata diagram). This part isn't real clear to me right now. My instructor was leading me through it and pointed out that it wouldn't work right, so maybe you can figure that out through the Alldata diagram. I was not able to print out the diagram showing the power supply routing, but I will try to get a copy of that tomorrow.



http://img130.imageshack.us/img130/7206/headlight2ik9.jpg



I was considering just replacing all the stock wiring with 12 ga through the fuse box, but I'm having accessibility problems, and I'm concerned about getting that involved into it, getting lost, and being stuck without headlights.

Thus bringing me back to the original question of being able to just run these bulbs off the stock wiring. Any suggestions?

Don't do this with the stock wiring. It is barely up to the task of running the stock 55W bulbs much less higher wattage ones. To even think about this you need to upgrade the wiring.
Other things to consider-
The Subaru lighting system is a common positive, switched ground setup. As you can see from the diagrams, the negative side of the circuit goes through the headlight switch and there is no relay on that side. This means that the switch has to carry all of the ground current for both bulbs. The added current from those high-watt bulbs could overheat and damage the switch in addition to the connectors and wiring.
If you take some measurements with a voltmeter you'll find that even with the stock lights there is already some voltage drop in the headlight wiring, particularly on the ground side due to the ground switching system. With higher wattage bulbs the drop will be much worse and you wouldn't get full power to the bulbs anyway.
Even if you did upgrade the wiring (most important would be adding relays on the ground side to take the load off the switch and directly ground the bulbs), the added heat from the higher wattage could discolor the headlight reflectors over time.
Finally you would be replacing bulbs often, these have a much shorter life than stock wattage bulbs.

I'd suggest that before you go crazy with major modifications or high-watt bulbs, try some simple tests and upgrades to the OEM setup. Some time spent with a voltmeter will identify where most of the voltage drop in the lighting circuit is, it will probably be on the negative side as I explained. Just adding relays to provide a more direct ground path for the bulbs may make a very noticeable difference in lighting performance even with stock bulbs. After that, there are some stock wattage H4 bulbs of the "+50" or "high efficacy" type that will produce more usable light without a blue color or added heat. Check the offerings at www.rallylights.com and www.danielsternlighting.com
And, if the lenses themselves are hazed or discolored this is costing you light output as well. I'm not sure if yours are plastic or glass, if they are plastic they can be polished to remove haze and yellowing and restore clarity.
If you take the time and effort to follow the steps above instead of just throwing those brighter bulbs in, you may be very surprised at the results in the end.

So would you suggest that I trace the wires related to the headlights and splice in 12ga wires to replace them?

As far as bulbs go, would you suggest one of these, via rallylights (http://www.rallylights.com/hella/H4.asp)?

This bulb is in the same high-efficacy family as our popular 64217 (65W H7). Extremely high performance from a bulb that is only very slightly above standard wattage. Excellent compatibility with the smaller, less heat-resistant headlamps and with stock vehicle wiring.

CP64205 Bulb H4 Bulb, 12V 70/65W Hyper with 2000/1350 lumens, by Osram, each $19.78

CP64206 Bulb H4 Bulb, 12V 85/80W Hyper with 2400/1750 lumens, by Osram, each $19.78

Are these the Osram Silverstars that I have seen mentioned time and time again?

So would you suggest that I trace the wires related to the headlights and splice in 12ga wires to replace them?

This misses the point I was trying to make. Just replacing the wires is not sufficient because of the switched ground system. To eliminate the load on the headlight switch and reduce the voltage drop, you'd need to add relays on the ground side.

As far as bulbs go, would you suggest one of these, via rallylights (http://www.rallylights.com/hella/H4.asp)?

The Osram "Hyper" bulbs are still higher than stock wattage although the 70/65's are probably safe if you upgrade the wiring. But you should be able to get nearly the same performance from the Hella +50's at stock wattage, and they're cheaper. Stay away from the 85/80.
Also note the life ratings, at 350-400 hours they won't last as long as stock or equivalent bulbs (most aftermarket bulbs won't) but they'll still last longer than the 80/100's.


CP64205 Bulb H4 Bulb, 12V 70/65W Hyper with 2000/1350 lumens, by Osram, each $19.78

CP64206 Bulb H4 Bulb, 12V 85/80W Hyper with 2400/1750 lumens, by Osram, each $19.78

Are these the Osram Silverstars that I have seen mentioned time and time again?

Those aren't Silverstars, the Silverstars are 60/55W. Don't think Susquehanna carries those but the Hella +50s should be a functional equivalent. Look at Daniel Stern Lighting for more choices.

Thank you for the information. I missed a few key points you made the first time I read it, but again, thanks. I picked up a set of Osram Silverstars, and I'll be rewiring the ground side of the circuit.

Does this sound right for wiring the relay?
85 - Power through "3" on stock headlight harness
86 - ground side of stock switch
30 - High or Low beam ground (1 and 2 on the stock plug)
87 - ground

I apologize if I seem to be beating this topic to death.