Am I making this too complicated?

[Legacy777]

I'm just not following the wiring diagram of the headlamps. I know subaru uses a common ground or something like that. I'm sure I could figure out what to hook up, but I'd like to understand how things are working. It's just not making much sense at all.

Anyone care to help me understand.

here's the wiring diagram
http://www.main.experiencetherave.com:8 ... g_(US).pdf

[vrg3]

Subaru doesn't use a common ground... they use a common +12v. That's the part that confuses some people. The "common" terminal of the bulb is supplied +12v, and the switch completes the ground on the other side of whichever filament is to be illuminated.

Do you want to replace some of your stock wiring for some reason? Cuz the simplest way to do this is to just use all the stock wiring (intact) to trigger your new relays (essentially putting the relay coils in place of the headlamp filaments). This is what I described in the thread titled "Brighter Headlight Mod."

If you like, I could explain the entire path that current takes in the stock headlight wiring, but it's not really important if you just do your wiring how I describe.

[Legacy777]

Ok....after I posted, I looked at things again, and yeah I see that it's a common +12v.

Another thing I was getting confused about is the lighting switch vs the high beam/low beam & passing switch.

Once I understood that the lighting switch is the thing you twist, and the other was the push/pull thing.

I understand how the low beam circuit works now, and how the high beam works.....however I'm still a little confused how the passing circuit works. Isn't both the low & high beam filaments on at the same time when you use the passing switch?

So just to confirm.....pin 3 would be my common +12v, pin 1 would be the high beam, and pin 2 would be the low beam?

[vrg3]

Yeah, the diagram's a little weird. It's also complicated by the fact that the headlamp relays are on the power distribution page of the manual and not on this page.

When passing, only the high beam filament is on. You can't burn both filaments of a headlight bulb; the wiring isn't meant for that much current and the bulb isn't meant for that much heat. If you're lucky, all that happens is the bulb burns out early; but if you're not, the wiring could catch fire and/or the bulb could explode violently.

That diagram is for a post-facelift, so I don't know if you want to use those pin numbers. You'd probably be better off using the wire colors. The left headlight's common wire is red/blue, and the right headlight's common wire is blue/white. The low beam wire is yellow/blue on both sides, and the high beam wire is red on both sides.

If you want to know which terminal is which on the bulb, use this:

http://www.graphics.cornell.edu/~v/pics/h4_base.png

[Legacy777]

So what is the diode for/do?

The wiring pin #'s are the same for the pre & post face lift headlights.

Your picture confirms that.

Thanks Vikash

[vrg3]

The diode makes it so your high beams don't turn on when your low beams are on.

See, since flash-to-pass has to work even when the headlights are on, it has to do two things: 1) turn on the headlight relays, and 2) turn on the high beam filaments. Both these things have switched grounds, so flash-to-pass has to ground both the relays and the high beam filaments.

But if you just connected the flash-to-pass pin on the switch to both the relays and the filaments, then you'd also be connecting the filaments to the relays, which would make the high beam filaments come on whenever the relays were turned on.

The diode isolates the high beam circuit from the relay coil circuit, preventing that situation and allowing them to function normally.

I hope that makes sense. In any case, I'll reiterate that you shouldn't need to worry about any of this.

As for the pin numbers, I suppose it depends on how you number the pins.

[Legacy777]

Thanks for the explanation. Yeah that makes sense.

Yeah I don't need to worry about it.....just curious