Headlights dim momenarily
Thread Starter
Pro
Joined: Jul 2003
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From: Dover AFB DE
Headlights dim momenarily
Tonight on the way home I noticed my headlights dimming momentarily. I noticed it after I flashed someone (low to high, back to low), then a couple of times later on. It's a 15 minute ride home from work.
I put the DIC on the battery voltage and it was reading 13.1v unless I put my foot on the brake or turn signals. Then it would drop to 12.8 and go back up to 13.1v.
When I pulled into the garage, I put my foot on the brake and the dimmed in concert with the brake lights.
Is this normal? What could be going wrong. I know the previous owner installed a new alternator. I don't know how many miles ago or when it was done. I also have left my European rear lights in, so I have 5 brake lights and 4 separate turn signals. Maybe this is the problem.
I put the DIC on the battery voltage and it was reading 13.1v unless I put my foot on the brake or turn signals. Then it would drop to 12.8 and go back up to 13.1v.
When I pulled into the garage, I put my foot on the brake and the dimmed in concert with the brake lights.
Is this normal? What could be going wrong. I know the previous owner installed a new alternator. I don't know how many miles ago or when it was done. I also have left my European rear lights in, so I have 5 brake lights and 4 separate turn signals. Maybe this is the problem.
Safety Car
Joined: Jul 2005
Posts: 4,275
Likes: 4
From: Vancouver WA
You may have a battery going bad. Take it and have a load test done on it. It can still have voltage and be weak from not enough amperage.
Also if your air-conditioner compressor puts a heavy load on the charging system and can make the lights dim when it kicks on. Did you have yout AC or Defrost on?
Also if your air-conditioner compressor puts a heavy load on the charging system and can make the lights dim when it kicks on. Did you have yout AC or Defrost on?
Last edited by RED99; Oct 6, 2005 at 12:23 AM.
Racer
Joined: Jun 2004
Posts: 319
Likes: 40
From: Hemet CA
I've noticed the dimming on my 2001 Coupe. I keep thinking that it's in response to accessory load somewhere but it's hard to pinpoint when everything's on and working fine. Kind of like the lights dimming in my old house when the refrigerator cycles on.
I wonder if it's the alternator cycling on/off or maybe some unknown accessory cycling on/off. Either way, it's mysterious and something for someone like Bill Curlee or Patches to explain. Not a problem - just mysterious.
Good luck...Bill
I wonder if it's the alternator cycling on/off or maybe some unknown accessory cycling on/off. Either way, it's mysterious and something for someone like Bill Curlee or Patches to explain. Not a problem - just mysterious.
Good luck...Bill
Race Director
Joined: Aug 2002
Posts: 16,730
Likes: 1
From: Redacted
They just do that.
The voltage regulator in the alternator is slow to react to sudden changes in load, like when you step on the brakes (brake lights come on) or when the AC compressor kicks in (electric clutch).
Other than redesigning the voltage regulator, there's not much you can do about it.
The voltage regulator in the alternator is slow to react to sudden changes in load, like when you step on the brakes (brake lights come on) or when the AC compressor kicks in (electric clutch).
Other than redesigning the voltage regulator, there's not much you can do about it.
Team Owner
Joined: May 2001
Posts: 87,408
Likes: 1,595
From: Western NY
Originally Posted by larrysb
They just do that.
The voltage regulator in the alternator is slow to react to sudden changes in load, like when you step on the brakes (brake lights come on) or when the AC compressor kicks in (electric clutch).
Other than redesigning the voltage regulator, there's not much you can do about it.
The voltage regulator in the alternator is slow to react to sudden changes in load, like when you step on the brakes (brake lights come on) or when the AC compressor kicks in (electric clutch).
Other than redesigning the voltage regulator, there's not much you can do about it.
This has been mentioned a couple of times in the past. Most C-5s seem to do this.
Safety Car
Joined: Jun 2003
Posts: 3,596
Likes: 8
From: Grosse Ile MI
Originally Posted by ronwc
You may want to try cleaning and tightening your battery connections -solved my simular problem -
Cured my dimming headlight and erratic voltage reading problems also.
Safety Car
Joined: Jun 2003
Posts: 3,596
Likes: 8
From: Grosse Ile MI
Originally Posted by jjcslynn
I put the DIC on the battery voltage and it was reading 13.1v unless I put my foot on the brake or turn signals. Then it would drop to 12.8 and go back up to 13.1v.
The momentery voltage drop is normal and .3 volts is not much to be concerned about. It's caused by a slight lag time in charging system. Do a search in C5 Tech (current and archives) for dimming head lights and you will find a wealth of info on the subject.
Last edited by stingrayl76; Oct 6, 2005 at 06:29 PM.
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From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
Originally Posted by Z06ufgrad2002
Yup, it's totally normal. Mine is caused by the air pump coming on and off. I replaced the OE battery with an Optima battery and it helpd quite a bit but, even that did not eliminate it 100%. 
Pretty common. Nothing to be too concerned about.
Thread Starter
Pro
Joined: Jul 2003
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From: Dover AFB DE
Headlights dimming
Originally Posted by RED99
You may have a battery going bad. Take it and have a load test done on it. It can still have voltage and be weak from not enough amperage.
Also if your air-conditioner compressor puts a heavy load on the charging system and can make the lights dim when it kicks on. Did you have yout AC or Defrost on?
Also if your air-conditioner compressor puts a heavy load on the charging system and can make the lights dim when it kicks on. Did you have yout AC or Defrost on?
