Why are my headlights dimming when braking? - Page 3 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 03-11-2013, 03:32 PM   #21
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where did you connect the wire to
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Old 03-11-2013, 05:30 PM   #22
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where did you connect the wire to
where the how to guide said to.
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Old 03-12-2013, 07:20 AM   #23
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i think i would take some measurements around the car, see what the voltage is in the car when putting on the brake. they might have had to small a circuit somewhere. might be beneficial to put the sense wire in the car where the loads are

you may have some water in some of the light housings. or water getting into the harness some were or the wire partially shorting to ground due to vibration chafing the insulation
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Old 03-12-2013, 01:44 PM   #24
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i think i would take some measurements around the car, see what the voltage is in the car when putting on the brake. they might have had to small a circuit somewhere. might be beneficial to put the sense wire in the car where the loads are

you may have some water in some of the light housings. or water getting into the harness some were or the wire partially shorting to ground due to vibration chafing the insulation
I have already checked all the light housings.. I know there is no water in them. I already had that problem a couple of years ago, replaced the backup light sockets.

So where would you suggest moving the sensing wire too? I would think the greatest load would be right where it'* at, where all the maxi fuses and relays are located.
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Old 03-12-2013, 01:52 PM   #25
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I believe the main issue is, the alternator is not strong enough at idle RPM to provide enough power to maintain a sufficient charge on the battery. Though your alternator may pass the bench test at Autozone, but they also ramp up the RPM beyond your normal engine RPM of 600-700. Usually this is due to a failing rectifier bridge. Just my 2 cents.
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Old 03-12-2013, 01:57 PM   #26
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I believe the main issue is, the alternator is not strong enough at idle RPM to provide enough power to maintain a sufficient charge on the battery. Though your alternator may pass the bench test at Autozone, but they also ramp up the RPM beyond your normal engine RPM of 600-700. Usually this is due to a failing rectifier bridge. Just my 2 cents.
It makes sense that the alternator isn't strong enough to keep up at idle, because at idle is the only time this stupid thing dims.

Is there any way to test the rectifier bridge? Or does that mean it'* off to buy a whole new alternator?
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Old 03-12-2013, 02:30 PM   #27
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If the cables and battery are truly in good condition, it may be possible to do a amp draw test on while a load was placed on the alternator. Basically, measure the amount of amps being drawn on the battery engine off lights on etc, say if its, 50 amps, start car up, allow to reach operating temp or 600ish RPM whichever comes first, then measure the amp draw with the same electrical load except, connect the clamp onto the alternator cable. If the value is the same or higher, and if you increase the RPM and the value goes down, then, yes, your alternator is dying.

I hope that made sense. Or you can read this one, but its using voltage which isn't a very good test. How to Test a Car Alternator
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Old 03-12-2013, 02:44 PM   #28
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If the cables and battery are truly in good condition, it may be possible to do a amp draw test on while a load was placed on the alternator. Basically, measure the amount of amps being drawn on the battery engine off lights on etc, say if its, 50 amps, start car up, allow to reach operating temp or 600ish RPM whichever comes first, then measure the amp draw with the same electrical load except, connect the clamp onto the alternator cable. If the value is the same or higher, and if you increase the RPM and the value goes down, then, yes, your alternator is dying.

I hope that made sense. Or you can read this one, but its using voltage which isn't a very good test. How to Test a Car Alternator
with an amp draw test, doesn't there have to be an open in the circuit and the meter placed in that open?
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Old 03-12-2013, 02:53 PM   #29
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You can buy the multimeters with the amp clamp that would go over cable. No cut an splicing or anything.
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Old 03-12-2013, 02:54 PM   #30
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