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Discussion Starter #1
Hi Everyone -

I'm a new 2012 Focus owner (US-spec) and new to this forum - great stuff here.

I have noticed that the amber marker (parking?) lights in the headlamps are brighter on the driver side vs. the passenger side. These are the bulbs that are in the upper corners of the headlamp units - located on the "outboard" side of the low-beam bulbs. The actual bulbs are completely visible through the headlamp housing.



I went so far as to measure the voltage going to each of the sides and confirmed that the driver side is getting a full 12v, while the passenger side is getting ~5v. The voltage difference between the two definitely explains the difference in brightness, so I'm guessing this is intentional by design. (The alternative is that I have an electrical fault somewhere).

However, since I've never had a car that did this before, can anybody else out there confirm this behavior in their 2012 US-spec Focus?

Thanks!
 

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Mine are perfectly equal in brightness.
Did you take the bulb out on the poor side? and stick it back in?
It may have some dirt or? on it..
Ir just have that resistance internally. I would think you would have to try another bulb in there.
It certainly should be a warranty covered issue.
 

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will take a look at mine tonight... hmmm...
 

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That wouldn't be by design, there is unwanted resistance somewhere in the circuit causing a voltage drop before or after the light. If you can find where that bulbs ground wire goes, go from there to ground terminal at the bulb, if you see any voltage readings doing this there is a problem with the ground side of the circuit. Hopefully it's just a weak ground connection. It would get a bit more complicated to have to test it up circuit of the bulb, but you'd want to do the same thing, go from the power wire terminal of the bulb to various points further up the circuit.

Or as Elizabeth said, this is certainly a warranty kind of issue and should be relatively quick for any decent tech to diagnose and fix.

You could swap the bulbs around if you want, but I doubt it's a problem with the bulbs since they're brand new.
 

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JUST checked mine to make sure it wasn't a running issue like the alignment of the spoiler:



looks the same brightness to me. anyone with issues, i think should get the dealer to look at it. any trained tech should be able to diagnose / fix the problem.

good luck, op. [cheers]
 

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Discussion Starter #7
Problem solved! It was the bulb. I replaced the bulb and all is now good - full brightness on both sides.

However I have a wacky theory about what was going wrong: a poor connection causing low voltage, a dim bulb, and premature bulb "failure". I learned that these bulbs (WY5W / 2827) are actually halogen bulbs. Halogens run on what is known as the "halogen cycle" where evaporated tungsten from the filament gets re-deposited back on the filament. This cycle can only work if things are hot-enough. If there's not enough voltage to the bulb, the cycle can't work. When I look at this bulb, the glass is noticeably darker than the bulb on the (working) driver side - my guess it's the tungsten that never got re-deposited back on to the filament.

I'm also guessing that there was a connection at the bulb base causing a poor, high-resistance connection - remember I was only reading 5v in my first check. After wiggling all the connections and making sure things were properly seated with the new bulb, all is good. That's my theory anyway!

And yes, this should've been a dealer warranty job, but the nearest dealer is about 30 minutes away from home/work and it was more convenient to try to chase this one myself. I'll admit that being an electrical engineer probably had a bit to do with this - professional pride and all...

Overall, I'm loving the new car!
 

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Problem solved! It was the bulb. I replaced the bulb and all is now good - full brightness on both sides.

However I have a wacky theory about what was going wrong: a poor connection causing low voltage, a dim bulb, and premature bulb "failure". I learned that these bulbs (WY5W / 2827) are actually halogen bulbs. Halogens run on what is known as the "halogen cycle" where evaporated tungsten from the filament gets re-deposited back on the filament. This cycle can only work if things are hot-enough. If there's not enough voltage to the bulb, the cycle can't work. When I look at this bulb, the glass is noticeably darker than the bulb on the (working) driver side - my guess it's the tungsten that never got re-deposited back on to the filament.

I'm also guessing that there was a connection at the bulb base causing a poor, high-resistance connection - remember I was only reading 5v in my first check. After wiggling all the connections and making sure things were properly seated with the new bulb, all is good. That's my theory anyway!

And yes, this should've been a dealer warranty job, but the nearest dealer is about 30 minutes away from home/work and it was more convenient to try to chase this one myself. I'll admit that being an electrical engineer probably had a bit to do with this - professional pride and all...

Overall, I'm loving the new car!
congrats on getting the issue resolved, thought it would be weird to have a dim marker light by design. [cheers]
 
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