Headlight low beams quit working

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Greg Bryan
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Re: Headlight low beams quit working

#16 Post by Greg Bryan »

You can look at your back issues of the Registry magazine - an article on headlight circuit operation was in volume 38-5, 1-2/2015 starting on page 74, or go to the on-line version
https://porsche356registry.org/system/m ... 1431541784
Troubleshooting the headlight circuit was in the following issue - 38-6, 3-4/2015, page 64, also available on line.
https://porsche356registry.org/system/m ... 1431541885
Greg Bryan

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Dave Wildrick
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Re: Headlight low beams quit working

#17 Post by Dave Wildrick »

Dave Wildrick wrote:
Larry Brooks wrote:Interesting. Have you tested your line voltage with the engine running at 2000rpm? An obvious place to check would be the headlight circuit.
I have not done this yet.
I'll check and let you know.
Low beams:
6.4 V at idle (750 r/m)
7.2V at 2,000 r/m
Dave Wildrick
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Mike Horton
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Re: Headlight low beams quit working

#18 Post by Mike Horton »

"3.Maybe your car experienced some shock or vibration that caused the hot low beam filaments to fail while the cold high beam filaments weren't affected."

...did you drive on Oklahoma roads?...
Mike

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Dave Wildrick
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Re: Headlight low beams quit working

#19 Post by Dave Wildrick »

Mike Horton wrote:"3.Maybe your car experienced some shock or vibration that caused the hot low beam filaments to fail while the cold high beam filaments weren't affected."

...did you drive on Oklahoma roads?...
Yes, but not with the headlights on.
Dave Wildrick
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Mike Horton
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Re: Headlight low beams quit working

#20 Post by Mike Horton »

Cessna Citation jets have the landing lights mounted on the landing gear struts, and the vibrations transmitted from rough runways, and stiff tires, lead to short bulb life... with those, occasional replacement, was not uncommon...

...we could turn the filiments vertically, and get better life,
Mike

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David Jones
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Re: Headlight low beams quit working

#21 Post by David Jones »

From the Instrument engineers handbook and from the recesses of my memory the following.
Shock and vibration, a low-voltage, high-current design should be used because it has strong filaments. Lamps of 6 volts or less usually have short, thick filaments, whereas lamps of more than 6 volts generally have longer and thinner filaments.
If I had known I would live this long I would have pushed the envelope a little harder.
Cymru am byth
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Jim Alton
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Re: Headlight low beams quit working

#22 Post by Jim Alton »

David Jones wrote:From the Instrument engineers handbook and from the recesses of my memory the following.
Shock and vibration, a low-voltage, high-current design should be used because it has strong filaments. Lamps of 6 volts or less usually have short, thick filaments, whereas lamps of more than 6 volts generally have longer and thinner filaments.
True. 6 V filaments should have twice the cross section of 12 V filaments (6 V filaments should have 1.4 times the diameter of 12 V filaments). It's not a likely failure but if both filaments really did fail simultaneously it has to be considered.

Maybe--somehow--the car managed to vibrate at a resonant frequency for the filaments.

I'm guessing though that it's far more likely one had been out for a while but unnoticed.
 
Jim Alton
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1958 Porsche 356A Cabriolet
1965 Porsche 911 Coupé
1966 Volkswagen Type 2
2003 Porsche 986 Boxster

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