Interior lights dim with brake, and blinker

[anothernord]

I've had this problem for some time now; Whenever I press the brake at idle, or turn on the hazard lights or turn signals, the dash lights all dim, including the dome lights. The engine also lugs slightly and vibrates under the load when the brakes are applied at idle. Does this mean there's a short somewhere, or is it a symptom of a bad battery?

Any ideas would be appreciated.

[Huffer]

Tends to happen when some electrical components wear out or get old - alternator, battery, grounds...

[jey]

I'd start by getting the battery and alternator tested - Autozone does it for free. Does your supercharger put any extra load on the motor at idle? Might be one of those rpm-specific vibrations that is a result of things not being perfectly in balance...

[anothernord]

^^ The SC doesn't have any load on the system when the clutch is disengaged. I'm pretty sure that the problem is my battery; Its 3 years old, and I have a lot of electrical load that gets placed on the system, in the form of 50 amps of lighting, and lots of other accessories.

[harrymaneuvers]

So I just noticed last night that I have these same symptoms... only at idle though.

I can progressively make my headlights/gauges get dimmer and dimmer by:

First stepping on the brakes.

Then most noticeably was when I would push one or two window switches (While still stepping on the brakes)

And then finally each fan speed that I go up (with ac on) seems to make my lights dim even further. (While still doing each of the above at the same time)

I am pretty sure that it isnt the battery because I just replaced mine for the first time since owning the car... that was about 60 days ago.

I am suspect of the positive battery cable. When I replaced the battery... the positive terminal was pretty corroded When I replaced the terminal... I cut off the old one plus about an extra 4 inches of the cable and it was still slightly corroded inside the actual cable.

But the fact that all of these go away upon higher revs makes me think that it is the alternator... which im almost sure is the original with 218k miles on it...

[Huffer]

^^ then your issue is the alternator, not the battery.

[harrymaneuvers]

Yea but out of the three places I took it too... all of them pretty much said the same thing... that it was the battery and that it couldnt hold a charge.

Either way this just gives me a reason to now do a big 3 with a new alternator.... I just scraped/cleaned most of my grounds.

I just cant figure out which subaru alternator is going to be the biggest upgrade but still be easy to install and not TOO much more than the $79 reman at the dealership.

I have read all the posts about the subject and know that I can get the tribeca alternator or an 07 sti alternator but do both of those require splicing a harness? Do they have the same diameter pulley as my stock??

I couldnt find any posts other than mentioning that they were options.

[Huffer]

There's not much point in going with a "bigger" alternator unless you're planning on being a cop or reserve firefighter with all the radio and light equipment - even then, the load is only temporary and they run heavy-duty batteries anyway.

Did you have the battery actually tested? as in removed from the car and tested? Or did these places just tell you the battery is fried based on your symptoms?

[harrymaneuvers]

All of the places wheeled out a computerized cart that checked both the alternator and the battery while still connected to the car.

So if I wasnt planning on putting in a huge sounds system... Then the remanufactured one should be more than enough???

The most I would be doiing would be DDM HID's and maybe a set of fog lights eventually.

If Huffer says I will be fine with going stock... then that is what I will do.

[deadend]

I feel like its the grounds. I haven't personally done it, but it seems like our cars didn't come perfectly grounded (from what I heard from older imprezas).

[anothernord]

See, I already have a full grounding wire setup, and I went through and cleaned all the factory grounds. I'm guessing its just a worn out battery. Any recommendations for a replacement?

[jey]

Autozone - comes with a decent replacement warranty

[chuckthefuk]

Its very common for automotive electronics to draw excessive power during use.

Even if you replaced the Battery, alternator, ground cables, cleaned and used dielectric grease, you will still have excessive draw during window operations, dash lights, dome light, headlights and braking.

There is no way around this even new cars have this issue

Example: When the turn signal is activated the airbag/abs/cel will dim when the indicator is in use.
Example: Using the window regulators cause everything to dim...

Also the reason why these issue go away at higher rpm is because your alternator is putting out more voltage during use. So if you use your windows at idle your drawing only 12v.. but when your at higher rpms your windows still draw 12v but because the alternator is outputting 13.*v there is no noticeable drop of voltage when your windows are used.

However idle running poorly is an issue on its own.

-Chuck

[harrymaneuvers]

So what type of alternator could I put in there so that at idle I am putting out 13+ V??

Isn't that the reason for going with the bigger alt? Or would the solution be to put a smaller pulley on the alternator (effectively causing it to spin faster at idle)?

[chuckthefuk]

there are none as far as i know....
-chuck

[jey]

So what type of alternator could I put in there so that at idle I am putting out 13+ V??

Isn't that the reason for going with the bigger alt? Or would the solution be to put a smaller pulley on the alternator (effectively causing it to spin faster at idle)?

You can use an alternator out of an STi or Tribeca that has more output possibly.

Don't mess with the pulley - at redline you may be spinning the alternator at higher speeds than it was engineered for.

[harrymaneuvers]

Well as of now I think I am just going to go with a stock used one with a 3 year unlimited mileage parts and labor replacement warranty.

[ouch1011]

The alternator will only put out 50-60% of its rated output at idle. I think that these alternators are rated at 90A, so figure 45-50A at idle. Thats headlights, ac/heater fan, and probably the stereo. A bad/weak battery will certainly compound the problem since it will either drop the voltage more once the alternator is overloaded, causing even lower output from the alternator as the voltage continues to drop, or it may actually draw current constantly rather than provide a power reserve.

Depending on where you live, 3years may be the lifespan on the average battery if it is very hot or very cold. Around here, we have pretty mild weather, so the average battery last 5-7 years. 3 years for the super crappy ones (Exide)

[anothernord]

Yep, sounds like a new battery is in order for me. We see 100+ days in the summer, and below zero during the winter for weeks.

[harrymaneuvers]

Well i couldnt tell how long the battery had been in my car... the label was covered in corrosion...

But it was at least 3 years... Not too bad considering it is 100 degrees down here at the end of september :smt017

I have a flex innovations big 3 kit plus grounding kit on the way. My negative battery cable was still corroded (internally) when I replaced the terminal and battery... so I figured if I am going to replace that one wire... I might as well do the rest.