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30th September 2008, 19:35 | #1 |
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Spurious bulb failure warnings
I wonder if anybody can give me a brief explanation as to how the bulb failure monitor works please.
Almost every time I use my headlights now, when I switch them off I get a spurious bulb failure warning indication the O/S dipped beam. Then sometimes as a result of switching the lights back on and then off again, or by pushing on the O/S light unit connector, or by going over a bump, the warning will cease. I've had the connector off the light unit and cannot see anything amiss. Any ideas please? |
30th September 2008, 20:06 | #2 |
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Sounds like the chaffing of the wiring that is spoken about on the forum, quite common seemingly on the offside as the harness passes over the bodywork behind the bumper
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30th September 2008, 20:17 | #3 |
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Wiring to both headlamps showed no signs of damage a few weeks back when I did the I/C "O" ring though, and I beefed up the loom with spyrowrap.
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30th September 2008, 20:33 | #4 | |
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Quote:
Sorry about that Paul. All I know is that the bulb failure system seems to measure resistance, that is why you cannot use LED's for sidelights unless you install a resistor. Other than that in the words of the dragons "I'm out"
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30th September 2008, 20:38 | #5 |
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The bulb failure system measures current drawn from the circuit to assess whether a bulb is working or not - hence an open-circuit or LED lamp (which is high resistance) indicates a blown bulb as no current drawn. I think that the problem as you describe it is a "flaky" connection issue. I once had such an intermittent fault in the rear o/s brake-light - I took the bulb out and cleaned the contact on the bulb and it sorted it out.
HTH
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30th September 2008, 21:12 | #6 | |
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Not at all. It's where I would have started.
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So, the fact that disturbing the multiplug sometimes cures it suggests a dirty or corroded contact at that position then. I thought it was a current comparator, except that it seems to be able to detect a failed bulb even when the lights are off - unless it sends a small current round the circuit continuously. Last edited by Raistlin; 30th September 2008 at 21:16.. |
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30th September 2008, 21:21 | #7 | |
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Exactly - probably using a Parametric Measurement Unit as used in testing leakage and o/c in semiconductors - injecting a small current into the circuit and measuring the load. Corrosion as you explain is what I would suspect too yes - good luck!
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