Headlamps dim when braking
Thread Starter
Racer
Joined: Aug 2001
Posts: 469
Likes: 0
From: Pasadena MD
Headlamps dim when braking
Well, I've been enjoying my mods for almost 3 years now and now I again need the forum's help.
My headlamps have begun to dim when I apply the brakes and then brighten when I release the pedal.
Also, the digital voltmeter is going a little crazy too. It has been varying between 14.2 - 12 volts while driving.
Any suggestions?
Ken
My headlamps have begun to dim when I apply the brakes and then brighten when I release the pedal.
Also, the digital voltmeter is going a little crazy too. It has been varying between 14.2 - 12 volts while driving.
Any suggestions?
Ken
Tech Contributor
Joined: Dec 2003
Posts: 19,384
Likes: 87
From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
The first things I would check are whether the battery leads are clean and tight and then clean up the grounds (G101 left and G102 right). I'd also have a load check done on the battery if its getting on in years. If its the OEM battery change it anyway. The 99 OEM AC Delcos could leak.
Last edited by DeeGee; Dec 31, 2008 at 04:07 AM.
Team Owner
Joined: Jul 2006
Posts: 22,190
Likes: 4,178
From: Kannapolis NC
Also check the red wire connection from the battery at the starter side. If that connection is loose or corroded, you will see the same symptoms.
The headlamps will quickly dim slightly when you apply the brake or press the power window switch even when nothing is wrong, but the voltage variation you describe is not normal.
The headlamps will quickly dim slightly when you apply the brake or press the power window switch even when nothing is wrong, but the voltage variation you describe is not normal.
Burning Brakes
Joined: Jul 2004
Posts: 866
Likes: 5
From: Jensen Beach FL
The first things I would check are whether the battery leads are clean and tight and then clean up the grounds (G101 left and G102 right). I'd also have a load check done on the battery if its getting on in years. If its the OEM battery change it anyway. The 99 OEM AC Delcos could leak.
Le Mans Master
Joined: Feb 2002
Posts: 6,937
Likes: 21
From: Waldorf MD
While I agree a load test is the BEST test for a battery and almost anyone who sells batteries will do it for free.
By checking the voltage accross the battery (with nothing on in the car) you can check the state of the charge, a 12-volt battery will measure at about 12.9 volts when it’s fully charged and about 11.4 volts when it is fully discharged.
By checking the voltage accross the battery (with nothing on in the car) you can check the state of the charge, a 12-volt battery will measure at about 12.9 volts when it’s fully charged and about 11.4 volts when it is fully discharged.
Le Mans Master
Joined: Aug 2004
Posts: 9,420
Likes: 8
From: Southern New Jersey, The wet part at the bottom
St. Jude Donor '08-'09-'10
I had similar voltage issues until this past summer I upgraded audio and (here's the tip!) did the "Big Three Mod". Search for this mod to the C5's wiring upgrade to handle audio amps etc. as it pertains to adding AWG 4 wire from the + battery post to the alternator output plus adding engine and chassis grounds again using AWG 4 wire and appropriate connectors. After doing this easy mod I see constant battery values in the expected 13.8-14.2 range. I would encourage anyone looking to improve on battery voltage to do this mod whether you are upgrading audio equipment or not. This mod doesn't modify the OEM wiring, but rather "adds" to it and could be reversed if desired. 
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Thread Starter
Racer
Joined: Aug 2001
Posts: 469
Likes: 0
From: Pasadena MD
I've been reading alot on electrical issues on the forum and the big three seem to be bad battery, loose connection to starter and corroded ground.......car's only got 62k miles so I don't at this point think it the alt/reg. thanks, I got some troubleshooting to do.
Tech Contributor
Joined: Dec 2003
Posts: 19,384
Likes: 87
From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
Let us know what you find. Often members get these answers but don't then follow up. Feedback is always useful
