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IowaCowboy
Lost in the Supermarket
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join:2010-10-16
Springfield, MA

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Re: [Help] Low beam headlights quit working

I would have noticed as all my trips end at the driveway and at the end of my driveway is a big white garage door that they shine on when I park the car at the end of the night.
nonymous (banned)
join:2003-09-08
Glendale, AZ

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It all depends. Headlights on simpler cars are usually not that bad if you find a airing diagram. Some stuff may not even be in the steering column as no room.
fixrman
From a broken heart to a hole in the sky
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join:2003-02-10
Hatboro, PA
·Verizon FiOS

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Let me just say, that as complex as vehicles get - I say vehicles, because all have changed, planes, trains, automobiles, trucks.

But as much as they have changed, they are basically the same. i'll likely get flak for saying it, but most of what is cars today are add-ons. The engine block is for all intents and purposes the same, performs the same function as do the pistons, crankshaft and the flywheel.

One of the biggest impediments to automotive repair is to throw a $2.00 repair at a $0.25 problem. When a problem presents, it is best to start at the basic level to diagnose it and go from there. It is called Strategy-Based Diagnostics, really or some may call it process of elimination.

Now, the more highly trained a person is, one can also throw plausibility in there. When someone has a good knowledge of how a system works, they may be able to skip certain steps. In your case, if the headlamps are controlled by a fuse or fuses, that is a good place to start. Why worry about the switch or delay timer when the fuse is blown? Why the fuse failed to open is secondary at this point. If the fuse is good it would have made sense to see if there was a voltage signal at the appropriate headlamp terminal. Why did I say signal? Voltage alone doesn't give enough information.

Let's say I am diagnosing this fault today. Checked the fuse - good, So I pull out a test light and I see I have a glowing filament. Well, everything must be good, right? Well, it is really sunny today so I may have not noticed that the filament was dim. I can get a test light to illuminate at some relatively low voltages. I put a DVOM in the circuit and I see I only have 5V; now, that is a problem - I have found a fault. Somewhere a wire is pinched or damaged and there is significant voltage drop. At this point, maybe I decide to take it to someone who knows more.

Perhaps you want to know why bulbs seem to fail too often. Perhaps when you connect the DVOM to the circuit with the engine off, the voltage is 12.6V. OK, so that is fine, but with the engine running the same circuit indicates 16.2 volts. That's a problem.

What I am saying is, all cars have high beam/low beam circuits consisting of at least two bulbs and up to four. In this case the high beam circuit indicates the switch is likely good, at least to a point. Now the weak point in an electrical circuit is always the mechanical portion, but for our purposes:




Follow the black arrows. All a schematic is - an electrical road map. Move the switch arrow to the left; you have Bat+ at the low beam socket terminal. You can diagnose other low beam faults from that point back. In that circuit, I'd be looking at the bulb(s) first, unless there were other clues.

TheTechGuru
join:2004-03-25
TEXAS

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You didn't specify which trim so I had to take a guess.

Hope this helps.
Quattrohead
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join:2005-02-09

Quattrohead

Premium Member

First car I bought when I came to the USA was a Dodge Stratus, seemed like a good car lol
Believe me, you would not know it if the head lights were not working.....a blown out candle throws more light than those lousy excuses for lights.
fixrman
From a broken heart to a hole in the sky
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join:2003-02-10
Hatboro, PA

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The low beam filaments burned open.
PrntRhd
Premium Member
join:2004-11-03
Fairfield, CA

PrntRhd

Premium Member

Exactly.
Headlights (halogen or incandescent) have a finite life and they can go bad one at a time or nearly at the same time. Which is why it is best practice to replace them in pairs.
dbamber
join:2003-02-07
Bandon, OR

dbamber to bmilone2

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Back in the 1970's I was a service manager at a Chrysler Plymouth dealer. I had an excellent mechanic that did electrical/tune up/etc. He stated that when a bulb that is paired with others burns out that the voltage rises feeding the remaining ones, and caused premature failure. I remember having many cars coming in for service with burned out headlamps only requiring bulb replacements to solve the problem. The customers were quite happy getting a small bill when they were expecting a larger bill for electrical issues.
chuckkk
join:2001-11-10
Warner Robins, GA

chuckkk

Member

That's true when both bulbs are due to fail. Remember that they have the same number of hours if they were original or replaced at the same time. The small voltage change would not cause "good" bulbs to fail.

aurgathor
join:2002-12-01
Lynnwood, WA

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aurgathor

Member

The voltage change, if any, depends on how much of the wiring is shared between the bulbs, and the voltage drop over those wires which is proportional to the wire gauge. In a well designed system the voltage drop should be negligible; in a cost reduced system -- it's anyone's guess.
aurgathor

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said by PrntRhd:

Exactly.
Headlights (halogen or incandescent) have a finite life and they can go bad one at a time or nearly at the same time. Which is why it is best practice to replace them in pairs.

In a span of about 30 years, I never had to replace a headlight in a pair, and I don't remember any car where I had to replace more than one. Automotive headlight bulbs are usually very well constructed and can last for a long time, at least in my cars.

IowaCowboy
Lost in the Supermarket
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join:2010-10-16
Springfield, MA

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I always replace headlights in pairs, even if just one is out. Someone I know told me he had an alternator go on one of his cars and it started doing all kinds of strange things.
System

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Anon

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This topic has been closed. Reason: run its course