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Old 4th February 2007, 01:33   #1
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Unhappy Right head-light too dim

My right head light has been glowing too dim since past few days. I know, this happens due to weak battery, but don't think, that's the issue. The start-up, power windows work fine, just as they used to, and the battery is new.

The bulbs were also recently changed. Could there be any fault with the wiring? Has anyone experienced this ?
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Old 4th February 2007, 03:36   #2
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check out the fuse.......
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Old 4th February 2007, 10:59   #3
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One headlight wont dim due to a low battery. The wiring is shot.
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Old 4th February 2007, 11:40   #4
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Its the relay aka cutout!
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Old 4th February 2007, 12:24   #5
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Or just the terminals in the holder are dirty.
Did you take out the bulb from assembly and light it up to see if its bright?
If it is that means your reflector, HL assembly glass is too dirty
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Old 4th February 2007, 13:05   #6
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i face the same problem...one headlight is a bit dimmer than the other one...have no cutout/relay...but what we colud do is change both the holders..
Will be going in the evening past sunset to do that...
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Old 5th February 2007, 22:21   #7
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>> One headlight wont dim due to a low battery.

That's not true. A car's electrical system is smart to divert more power to one of the headlights in case of a weak battery. I've observed this with my old fiat too. It's usually the left headlight that receives more power, for some reason.

Anyways, will take the car to a mechanic and sort it out soon.
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Old 6th February 2007, 12:11   #8
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Have heard this explanation for the first time. Can anyone throw some more light on this phenomenon?

Quote:
Originally Posted by amu1983 View Post
>> One headlight wont dim due to a low battery.

That's not true. A car's electrical system is smart to divert more power to one of the headlights in case of a weak battery. I've observed this with my old fiat too. It's usually the left headlight that receives more power, for some reason.

Anyways, will take the car to a mechanic and sort it out soon.
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Old 6th February 2007, 12:27   #9
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its wrong.

well just check the wiring and connectors, especially the grounding for your "dim" headlights, also are u running stock 55/60 or upgraded?
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Old 6th February 2007, 12:53   #10
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Quote:
Originally Posted by amu1983 View Post
>> One headlight wont dim due to a low battery.

That's not true. A car's electrical system is smart to divert more power to one of the headlights in case of a weak battery. I've observed this with my old fiat too. It's usually the left headlight that receives more power, for some reason.

Anyways, will take the car to a mechanic and sort it out soon.
Smart? What smart.
All the electrical system does is connect the headlamps to battery via a relay.
No advanced ECU or something where.
When battery goes both headlamps will go dim.
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Old 6th February 2007, 12:57   #11
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The relay could be designed to cut down the power to the right bulb to avoid glare to the oncoming vehicles.
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Old 6th February 2007, 14:01   #12
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Quote:
Originally Posted by esteem_lover View Post
The relay could be designed to cut down the power to the right bulb to avoid glare to the oncoming vehicles.
Havent seen anything like that in any of the cars whose electricals I know somewhat.The only way to cut power would be to add a resistor in the right headlight circuit so that you get lower voltage on the bulbs.
So you are running a 12V bulb on maybe 10 volts, which nobody would like to do.
So the only thing could be using a lower wattage bulb on the right side headlight, which is not the case in any of the cars.
Most cars in India come with 60/55W 12V Halogens now in case of H4
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Old 7th February 2007, 21:09   #13
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Update - The battery is weak, and is due for change.

My bulbs are standard 60/55W.

To those who don't believe the 'magical' phenomenon, the explanation is very simple. Each bulb has two filaments - high beam and low beam. Normally, only one of them glows and entire 12V is applied on one of the filaments. When the battery goes down, a simple electromechanical switch causes the two filaments to get connected in series (one after another), and 12 V is applied onto both. Thus, each gets only 6 volts. Hence the dimming. The left bulb is given a higher 'priority' and is dimmed in such a manner only if the battery is really down. The right bulb is first victim.

Even the old fiat does this.
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Old 7th February 2007, 22:33   #14
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So how is this preference given? If you simple connect two bulbs of equal resistance in series both will get the same voltage.
Basic physics.
I would really be interested in knowing how a simple electromechanical switch "gives preference".
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Old 7th February 2007, 23:21   #15
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But so far I believed that if the car battery is weak and can not hold sufficient charge, major problem is to start the engine. Once the engine is running, the alternator produces enough voltage/current to drive the electrical. (though I read on ICE section that Sam had encountered a sound quality issue in his car because of weak battery). So headlight also should get sufficient voltage/current to run at optimum ( a 60/55 factory spec). Also I donít see any benefits of running both the filaments of the bulb in series. At least on my Santro it has no such 'feature'.
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