[rasterman]

The dimming effect you have observed is ordinary and common to quite a few Subarus...

If it bothers you to the point where you want to do something about it, I might suggest converting to LED brake lights- the reduced current draw will make for less of a voltage drop.

I haven't seen an aftermarket voltage regulator.

For later models, you could consider using freeSSM to artificially raise the idle.

 

[Zioncanyon]

The dimming effect you have observed is ordinary and common to quite a few Subarus...

If it bothers you to the point where you want to do something about it, I might suggest converting to LED brake lights- the reduced current draw will make for less of a voltage drop.

I haven't seen an aftermarket voltage regulator.

For later models, you could consider using freeSSM to artificially raise the idle.

Are LED brake lights just a bulb replacement solution? Has anybody on this board actually done this with a result that solves the problem?

Is the dimming also related to the ABS, Battery dash lights coming on intermittently?

 

[rasterman]

Are LED brake lights just a bulb replacement solution? Has anybody on this board actually done this with a result that solves the problem?

Is the dimming also related to the ABS, Battery dash lights coming on intermittently?

LEDs are replacement bulbs. They draw less power, so the voltage drop would be much less noticeable- perhaps imperceptible.

The battery light illuminates when voltage has dropped below a certain threshold. The ABS light will also light up when voltage drops below a different (usually slightly higher) threshold. ABS requires electricity to work, so when the system thinks there isn't enough electricity there is a legitimate cause for concern and the light comes on.

You shouldn't be seeing the battery or ABS lights during any normal operation other than the self-test at startup. If you are seeing them, something is not up to spec with your electrical system.

 

[burnout8488]

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.

 

[jp1203]

My 2004 H6 didn't do that, and I believe it was a 100 amp alternator. It couldn't quite keep up if I had all the heated things, lights, blower fan, etc. on at once while idling though, but I guess that's to be expected. Not sure if it would work or not. I imagine you'd have to try to move brackets over at the least.

The 05 could have a higher output alternator. I think the H6 alternator went to 110 amps in 2005, not sure about the H4.

 

[burnout8488]

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.

 

[SE95]

The headlights don't dim on my '04 when I hit the brakes. But I do notice the blower fan turns significantly slower when I apply the brakes. It also spins up a lot faster under acceleration. Also... try turning on your four ways at night while you have the door open. See if your dome lights get brighter and dimmer, in-sync with the four ways. Mine do. I've also noticed at idle sometimes when I have the dome lights on, the main dome will kind of strobe a little bit. If I rest my foot on the gas pedal and kick the idle up just a little bit, it stops.

 

[OldStyle]

My '03 H-6 doesn't dimm either. Strange that it's an issue at all.... Must be a regulator issue?

 

[burnout8488]

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.

 

[rasterman]

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

That change could come with other consequences- MPG hit or reduction of alt life from extra wear when at higher RPMs.

I'm not suggesting you shouldn't do it, because it probably would solve the problem... just be ready to support the trade-off.

 

[jp1203]

That, or the H4 alt is undersized (90A) and the H6 is just right. (100A)

Especially interesting because many H4 Outbacks of that vintage had the same power options that the H6 models did (heated seats, mirrors, wiper deicers, power driver's seat, etc.).

 

[cardoc]

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.

 

[plain OM]

Bad grounds cause this.

Indeed.

It can be confirmed fairly easily with a digital multi-meter that can read down to 0.01 Volt. Start the engine, turn on load such as lights and heater fan, then measure the Voltage between the battery negative post (not the cable clamp) and a) the engine block, b) the alternator case, and c) the car body. (Be sure to scrape the surfaces to ensure a good contact.) Do this with the engine idling, with it running at around1200 rpm, and again at around 2000. With good grounds the Voltages will be just a few hundredths of a Volt. If any of the measurements is much higher and especially more than one or two tenths of a Volt, there's too much resistance in the ground circuits.

When there's resistance in the ground, the alternator cannot charge the battery properly, and then when the engine speed drops, and the alternator output drops along with it (this is shown in the specs), the system Voltage goes down quickly.

This is but one of the tests that could be carried out when diagnosing a dimming symptom, or to check the "health" of the charging system.

The addition of the large gauge cable bypasses the existing grounds, thereby ensuring a good path.

 

[burnout8488]

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.

 

[burnout8488]

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?

 

[cardoc]

By "what's worked for me" do you mean it fixed the dimming issue 100%? Or did it improve it markedly?

It corrected a lot of issues. My VDC came from Boston. A lot is rust at ground lugs, undercarriage bolts, etc.. One of the first things I did was clean up every ground in the engine compartment. The conductivity measured excellent only losing 50 amps between the battery and block and 75 between the battery and firewall. Dimming went away. I added in the 4 ga and it improved to a 40 amp loss to the body. This also helped a great deal when I overhauled the sound system.

Any time you reduce electrical flow loss, its an improvement. Corrosion is an inhibitor. Silicates are inhibitors. Loose connections. But you also have to have a good source and that is the battery.

Upon installing the SC, I added more grounding to handle the loads I created with added sensors, gauges and the 2 cooler pumps. I also now use a deep cell battery.

 

[burnout8488]

Excellent info, thank you. That should work good for my stock H4!

 

[burnout8488]

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

 

[cardoc]

I add grounding to a lot of cars. All makes/models when the need comes up. What you should try is a cable from the battery to the block. Or, bolted right up to the alternator bracket. Or, you could go to the bolt at the bottom of the AC. Still leave the one you put on the chassis.

Have you cleaned the grounds on the firewall?