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Electrical Tech: Wiring, turbo timers, electronic boost controllers, gauges, fuses, wiring harnesses, wire tucks, car audio, and all other electrical component discussions.

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Old 01-09-2011, 06:51 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #1 (permalink)
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Lights dim when press brake


So i noticed today that if im sitting at idle somewhere, if i turn my heater on to number two and have my lights on; my rpms will drop by like a 150.

Also when i press the brake down, my headlights will dim along with my dash lights.

It doesn't dim them alot but it doesnt enough to notice..

The Alt is new, all new fuses, no system ether and nothing running straight off the battery... Do you think it could be my terminals of the battery?

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Old 01-09-2011, 06:56 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #2 (permalink)
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Could be; or could be a bad ground. I had a similar problem except that the lights would dim an the coolant gauge would peg hot when stepping on the brake. Ended up running a new ground inside the car and that took care of it.


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Old 01-09-2011, 07:01 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #3 (permalink)
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hmmm. How many grounds does our 2gs have? and do you know if theres a section on here or a old post with each ground placement?
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Old 01-09-2011, 07:40 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #4 (permalink)
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check alt and battery wires to c if they are loose. also when idleling turn on your dome light if its flickering your alt is bad.


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Old 01-09-2011, 07:42 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #5 (permalink)
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i had the same problem but my radio would turn off if i had too much stuff on. last place i checked was the terminals .. i could move the negative with my hand

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Old 01-09-2011, 07:49 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #6 (permalink)
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Bad ground some where. Or the break boosters use a lot of vacuum I notice. When I push on my breaks my idle swoops up and down. But its just trying to suck in a lot of vacuum. Maybe look in too getting a aftermarket break booster.
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Old 01-09-2011, 10:20 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #7 (permalink)
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Quote:
Originally Posted by spawn87 View Post
check alt and battery wires to c if they are loose. also when idleling turn on your dome light if its flickering your alt is bad.
No dome light, sunroof.

Quote:
Originally Posted by adamsg View Post
i had the same problem but my radio would turn off if i had too much stuff on. last place i checked was the terminals .. i could move the negative with my hand
i can move my battery negative with just my hands.. i remember i forgot to tighten them last time i replaced battery when she died..

think that could do it? i mean im gonna fix it tomorrow but since im on here ill just ask haha

Last edited by 98mitsubishigst; 01-09-2011 at 10:21 PM. Reason: Auto-merged with previous post to prevent "bumping" within a 24 hour period Tips on avoiding the auto-merge feature - http://www.dsmtuners.com/forums/faq.php?faq=vb_faq#faq_bumping
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Old 01-09-2011, 10:25 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #8 (permalink)
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i partially agree on a bad ground, but if you find out thats not the problem then maybe you might have a bad "new" alternator or a worn alt. belt or both. causing it not to crank enough amps to power all of the above. test it!


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Old 01-09-2011, 10:45 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #9 (permalink)
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Could be a bad "new" alt like ^^^ said. Also loose terminals will definitely do it. Get them tightened.

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Old 01-10-2011, 02:35 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #10 (permalink)
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Quote:
Originally Posted by 98mitsubishigst View Post
No dome light, sunroof.
well you still got the lights on your rear view mirror dont you? thats your "dome light"


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Old 01-10-2011, 06:48 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #11 (permalink)
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ooo i getcha. ill check it tonight.
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Old 01-10-2011, 07:18 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #12 (permalink)
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You'll always notice some dimming of the lights. Our factory alternators are really weak, 65 amp units (Canadian market: 75 amp). By the time you add up all the power consumption going on while your car is running, the sudden draw from brake lights and the drop in rpm usually associated with slowing down is enough to make the lights dim a bit. This can be more pronounced if you run an underdrive pulley.

To minimize the affects, check your grounds and make sure you battery terminals are clean and the cables are on tight. Some people see some reduction in the dim by going to a better battery. It also helps to get an upgraded rewound alternator that puts out more amps. I saw a nice improvement by running a 140 amp unit. Our ground cables are now 12 years old at the youngest. I also saw some improvement by making new ground cables for all the existing ones. You may also want to check your cable coming off the alternator itself. It's actually two 8ga wires run in parallel. I replaced that too when I installed the higher output alternator.


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Old 01-10-2011, 01:38 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #13 (permalink)
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I would definatly check into putn a bigger alt on it

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Old 01-10-2011, 01:51 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #14 (permalink)
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Could be bad battery, bad ground wire, or the new alt would be bad as well.


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Old 01-10-2011, 01:54 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #15 (permalink)
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Quote:
Originally Posted by knochgoon24 View Post
You'll always notice some dimming of the lights. Our factory alternators are really weak, 65 amp units (Canadian market: 75 amp). By the time you add up all the power consumption going on while your car is running, the sudden draw from brake lights and the drop in rpm usually associated with slowing down is enough to make the lights dim a bit. This can be more pronounced if you run an underdrive pulley.

To minimize the affects, check your grounds and make sure you battery terminals are clean and the cables are on tight. Some people see some reduction in the dim by going to a better battery. It also helps to get an upgraded rewound alternator that puts out more amps. I saw a nice improvement by running a 140 amp unit. Our ground cables are now 12 years old at the youngest. I also saw some improvement by making new ground cables for all the existing ones. You may also want to check your cable coming off the alternator itself. It's actually two 8ga wires run in parallel. I replaced that too when I installed the higher output alternator.
This post sums it up perfectly. In a lot of cars you'll see some dimming of the headlights or interior lights when you are drawing a lot of power and do something else like push in the brake pedal or hit the window button. As long as it's not excessive and very noticeable, I wouldn't worry about it. Otherwise do what is mentioned in knochgoon24's post.


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