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Old 10-16-2005, 11:10 PM   #1
resident1155
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Unhappy Interior lights dim+bad idle= ...headlights?!

The first thing I noticed when I got my 2002 Impreza 2.5RS was the interior lights would dim when I turned on the headlights. Specifically, the clock almost becomes unreadable if I put the headlights on during the day. Also, when I turn on the lights, the idle drops from 500rpms to about 400rpms. At this point the idle becomes rougher, as anything below 400rpms and it would probably stall. I just had a 60,000 mile tune up so...ya I don't know why this is happening.

One of my theories is that they used to thin gauge of wire for the ground/power that run from the fog lights, but I can't be sure. As far as the idle dropping...that makes me think the alternator is on its way out or maybe the "magic 3" wires need to be upgraded.

I really hate taking my car to the dealership because they waste too much time. I do remember reading something about this in a thread but it didn't really explain my specific problem. Any help is appreciated. Thanks
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Old 10-16-2005, 11:12 PM   #2
WR^2X
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I have nothing to offer, other than you'll get a lot more help by posting in the Electrical and Lighting forum. But don't worry, one of the mods for this forum is really good about moving threads to the appropriate forums.
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Old 10-16-2005, 11:13 PM   #3
armand1
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Could be a bad battery -- take it in to Autozone or similar to have them do a "load" test on the battery.
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Old 10-16-2005, 11:15 PM   #4
adeliciouspizza
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the clock is supposed to dim when the lights are on
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Old 10-16-2005, 11:18 PM   #5
njskatchmo
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This may be stupid, but did you try spinning the little dial that increases the intensity of the interior lights?
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Old 10-16-2005, 11:22 PM   #6
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bad alternator?? get a multimeter and see if you have enough voltage going thru your alternator...
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Old 10-16-2005, 11:38 PM   #7
rice h8r
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I also think it could be a bad battery. Happened to my dad's LS400. The car wouldn't start and when I turned on the headlights, the inside lights would go very dark. Also the VSC warning light came on. We put in a brand new battery and all the problems went away including the VSC warning. We were lucky that it wasn't a major problem with the VSC. lol.
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Old 10-17-2005, 12:29 AM   #8
resident1155
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I don't think the clock is supposed to dim when the lights come on. I have a digital voltmeter and I'm going to test the line tomorrow. And yes, I tried spinning that dial to increase intensity. Also, I've been in a car before when the alternator is crapping out, and this is not the case for my car. Going to go post now in the electrical forum. Thanks for the help everyone.
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Old 10-17-2005, 07:49 AM   #9
MDRex
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The clock does dim when you turn the headlights on. There is a mod to make it stop dimming. Just pull the clock out and there is a connector pin on the back you can bend over and the clock never dims again.

Also check the dimmer dial first, it's one the left headlight stalk.

Also, the idle should be around 750, not 500. Try a home made grounding kit, helped my idle smooth out a little.

Go to scoobymods.com and look up grounding kit and clock dimmer mods.
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Old 10-17-2005, 08:56 AM   #10
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Bad: battery, alternator, ground


Start with cleaning the grounds.. then have the charging system load tested by an experienced mechanic (not at autozone) and then decide if you need an alternator or battery or both.
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Old 10-17-2005, 10:43 PM   #11
resident1155
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I bought the grounding kit on ebay and put it in today...noticed less hesitation but the idle still drops when I turn the headlights/fog lights on (especially the fog lights). I'm going to test the line tomorrow when I have more time..
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Old 10-19-2005, 06:01 PM   #12
resident1155
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ok I tested the battery and alternator with my voltmeter. Both read 14 volts at idle with the lights OFF. I had a friend turn the lights on while I was doing the testing. I found a 1 volt drop from the battery when I turned the lights on, but the volts did return to normal (14v). From the alternator I found a 4.5 volt drop but, there too, the volts returned to normal.

I am assuming this means the alternator has low amp output, but is still usable and working properly? I am curious to know if upgrading the power wire to the battery would help with this problem or if the alternator/battery combo should just be upgraded. Anybody have input on this??

Last edited by resident1155; 10-19-2005 at 06:07 PM.
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Old 10-19-2005, 06:48 PM   #13
rexxer
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Don't use the clock as a judgement point. It will dim as stated before. As for the rest, search for "grounding mod". That should help.
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Old 10-19-2005, 08:01 PM   #14
resident1155
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I did the grounding mod...it didn't help this specific problem.
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