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Lights aren't so bright

Taro Deneve
10/10/2011 03:52 PM EDT

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Resistor_Smoker
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re: Lights aren't so bright
Resistor_Smoker   11/6/2011 7:24:11 AM
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The car was a Daihatsu Charade, a 1990 model. The lights did work by switching the ground connection, but I guess that the lights were built for positive supply switching since they were fed with +12 V to the ground connection and the high and low beams went to the ground.

JobT
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re: Lights aren't so bright
JobT   10/27/2011 12:10:13 AM
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Talking of strange car wiring faults and quality control, on one occasion the fault showed itself as a dimming of the clock display when the brake was applied. After much head scratching and work I finally found that one of the double filament rear lights had a short between the filaments inside the bulb. I never quite worked out why the clock display was affected, but replacing the bulb fixed it.

wu0f
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re: Lights aren't so bright
wu0f   10/19/2011 12:33:16 PM
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On several of the newer cars I have had occasion to work on I have found that the lights all work by switching the ground. That way the computer knows what is working or not.

Oh_Roy
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re: Lights aren't so bright
Oh_Roy   10/18/2011 9:59:34 PM
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I like the story

David Ashton
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re: Lights aren't so bright
David Ashton   10/17/2011 11:45:24 PM
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" I still find that odd and that both went off and on at the same times." That's called Murphy's law... ;-)

Duane Benson
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re: Lights aren't so bright
Duane Benson   10/17/2011 11:28:21 PM
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I had a case a while back where both low beams were intermittent. The high beams always worked but sometimes the low-beams didn't. It was all the more difficult to troubleshoot because sometimes just turning the car off was enough to cause the lights to start working again. Eventually, I was able to verify that the switch was working, even when the lights were not. What really confused me was when I both verified that the terminals at the lights had a good 12V and both grounds seemed to be pretty darn close to zero ohms. Eventually, just for kicks, I replaced one of the headlights. Suddenly, only one headlight was intermittent. I replaced the second one and the problem went away completely. Looking closely at the bulbs, I could see that both had a broken filament that would lay down and make physical contact but could easily be jostled loose. Somehow, I had broken both filaments at the same time in the same manner. I still find that odd and that both went off and on at the same times.

WKetel
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re: Lights aren't so bright
WKetel   10/15/2011 1:17:36 AM
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ON the car with the headlights problem, I wonder if the headlight switch was originally intended to be switching the ground return for the lights. I can see that it would take less wire to control them that way, and it could avoid the problem of rusty ground connections at the lights. It would be interesting to know what make of car it was.

WKetel
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re: Lights aren't so bright
WKetel   10/15/2011 1:13:53 AM
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Liketobike is certainly correct about quality. Each generation of product is less robust and dependable, with new features that are useless and performing the intended task less adequately than the previous generation. So I repair the old one because I don't want the new one because it does not provide the function that I am looking for. Progress is seldom improvement in this era.

bk11
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re: Lights aren't so bright
bk11   10/14/2011 10:01:04 PM
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Poor grounds have been wreaking havoc in cars forever. In my first car, a 1970 model, all the lights would occasionally dim when I hit a bump or moved the auto trans shift lever. I searched all over for the culprit, using the vehicle schematic (all one page of it) for help. I finally found the problem working under the hood at night when I saw sparks jump across the well-worn transmission shift linkage! Since the engine, trans, rear suspension, and exhaust all mount with rubber bushings, a failed ground strap from the motor to the body caused the entire drivetrain to be isolated from the chassis. A simple fix after weeks of fruitless troubleshooting.

LiketoBike
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re: Lights aren't so bright
LiketoBike   10/14/2011 6:44:38 PM
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I must be entering old-fart-hood :-) Half the time at least, I want the old but still-working gizmo because I am more familiar with it, or it works better, or the new one omits some feature I want, or maybe I just have a nostalgic attachment to it (e.g., it belonged to a family member). Maybe this ties into the quality thread :-)

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