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Discussion Starter · #1 ·
I just read some threads on this forum from back in '04, it seems the dimming lights problem was normal on these cars even when new.

Since then:

Has anyone ever fixed this issue? Are there members here that don't have their headlights dim when they hit the brake pedal? Every bulb, interior and exterior, on my '01 dims when I hit the brakes, or even use my turn signals.

My OB has a brand new battery, and the alternator was replaced about a year ago. Clean terminals, all of the grounds I've seen look fine and have been unbolted/reattached.

If there is an alternator available that is higher output, or has a better voltage regulator that will solve this problem, I am all ears.

Back in '04 a Canadian member found that all of the new Legacy/Outback models on his dealer's lot exhibited this same problem. I am hoping that since then, a better alternator or a homebrew fix has been developed to remedy this. When tapping the gas pedal, all of the lights brighten, so it is obviously an issue with the charging system being inadequate at idle by design.

Discuss!
 

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Discussion Starter · #5 ·
Gotcha, that's kinda what I was looking for. Thanks for the input. If it happens with everyone, then I guess I can't do much about it aside from getting a custom higher output alternator, which isn't feasible for this car.

I'm not sure if mine is particularly weak, or if it's just the nature of the beast, but it happens with individual turn signals too. LED is a good idea, but I wish I wouldn't have to replace every single bulb in the rear of my car to try to alleviate this.

Looks like 90A is the stock alternator output, is there a direct-fit higher-amp application, like a 100A from an H6? (won't physically fit, right?) Or a later model H4 that used 100A? Maybe my aftermarket alternator just sucks? If I went with a Bosch or Denso replacement, are those common aftermarket alternators for these?

My '05 Legacy did not have this issue, I suppose this was fixed in '05 with the new generation.
 

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Discussion Starter · #7 ·
Interesting - it does seem that the issue is isolated to the 2.5 models, unless it isn't as widespread in H6 cars. Would be cool if the H6 alt was a direct swap but I don't believe it is.
 

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Discussion Starter · #10 ·
That, or the H4 alt is undersized (90A) and the H6 is just right. (100A)

Subaru must have not bothered to do anything about it until '05, sucks there isn't an updated part that solves this. I'm having a hard time accepting this as normal when I've owned much older cars that are fine in this area.

A smaller (overdrive) pulley would theoretically solve this issue if one can be sourced.
 

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Discussion Starter · #15 ·
The addition of a heftier ground has crossed my mind. I am surprised this isn't a more widespread complaint, given that they all do it it some extent. Perhaps I'll try adding a new engine-->battery and battery-->firewall ground this weekend when I'm home and report the results.

What about the factory grounding makes it weak compared to other vehicles that do not exhibit this symptom?

Again, this issue doesn't seem to occur on the H6 models, and they have a higher output alternator. Is the beefier alternator masking poor grounding (you would expect to see problems still) or is the H6 a better grounded vehicle? It seems that adding more grounds to an H4 model is essentially trying to milk the undersized alternator for all its got, which isn't enough if the H6 is just fine with 10 more amps.
 

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Discussion Starter · #16 ·
Bad grounds cause this. The system can only pull from what is available. What's worked for me is adding a 4ga cable from the battery to the firewall. It increases ground conductivity and helps with power flow. The cable is available at most parts store and you can get it with eyelets on both ends to make it easy.
By "what's worked for me" do you mean it fixed the dimming issue 100%? Or did it improve it markedly?
 

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Discussion Starter · #19 ·
Added a ground from the negative to the chassis - didn't have a cable long enough to reach the firewall. In any case, the ground from the battery to the chassis here looks to be an 8ga originally, I upgraded to a 4ga. Sanded the chassis to bare metal here as well.



No change whatsoever. Headlights/interior lights dim when the brake is pressed, then eventually creep back up to normal brightness after a few seconds of holding the brake pedal. Does this mean the voltage regulator is trying to catch up after the increased load? With every accessory turned on (heated everything) I am showing 12.55 volts at the battery. Normal? @ Idle with nothing on, 14.7v.

Cardoc, have you ever added grounds to an H4? Perhaps you aren't having the dimming issue because your vehicle is an H6 with the stronger alt?

I also replaced the alt today for kicks, no change either. My old alternator put out 14.7v, the new put out 14.2. At least I have a good excuse to bring it back!

This is the alternator that is currently in the car: http://shop.advanceautoparts.com/we...ps-worldwide_19850490-p?searchTerm=alternator
 

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Discussion Starter · #21 ·
Yup, I removed the ground straps in the engine bay to check them and they were all clean, sprayed them with carb cleaner to degrease, wiped down and scuffed, then reattached.

This ground cable should reach the alt bolt, perhaps this may be a more effective place to reinforce the grounding. I'll play around with it tomorrow! :)
 
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