Fog light issue
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Cloggy Saint
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I've just noticed that one of my front fog lights is much duller than the other (or one is much brighter than the other, not sure!). Both have the correct 7.5A fuse so what could be the fault? Do the bulbs have a double filament?
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Brianmoooore
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Just ordinary H3 halogen bulbs with one filament.
Turn the foglights on (so that you can see if the problem is 'accidentally' cured while working), remove the dim light (remove blanking plug halfway down the glass, undo the screw revealed, and pull the whole light out), remove the circular access cover over the bulb, turn the lights off, allow to cool, and check whether the 'glass' of the bulb is badly blackened.
If it is, then problem solved.
If not, then replace it, turn the lights back on, connect the black lead of a volt meter to a good body earth and measure the voltage on the metal base of the bulb and the centre wire.
One should read zero volts, and the other 12 volts +, but in your case one will be different.
If one wire measures 12 volts, and the other somewhere between 0 and 12 volts, then the light isn't being earthed properly. Check out the earthing terminal low down on the front LH inner wing.
If one wire measures 0 volts and the other somewhat less than 12 volts, then there is a poor connection between the fusebox and the light. Check the fuse pins for corrosion first of all, then the plug at the foglight.
Turn the foglights on (so that you can see if the problem is 'accidentally' cured while working), remove the dim light (remove blanking plug halfway down the glass, undo the screw revealed, and pull the whole light out), remove the circular access cover over the bulb, turn the lights off, allow to cool, and check whether the 'glass' of the bulb is badly blackened.
If it is, then problem solved.
If not, then replace it, turn the lights back on, connect the black lead of a volt meter to a good body earth and measure the voltage on the metal base of the bulb and the centre wire.
One should read zero volts, and the other 12 volts +, but in your case one will be different.
If one wire measures 12 volts, and the other somewhere between 0 and 12 volts, then the light isn't being earthed properly. Check out the earthing terminal low down on the front LH inner wing.
If one wire measures 0 volts and the other somewhat less than 12 volts, then there is a poor connection between the fusebox and the light. Check the fuse pins for corrosion first of all, then the plug at the foglight.
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Cloggy Saint
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Cheers Brian, that's tomorrow sorted! I should probably add that the light in question wasn't working at all until I changed the fuse and then it worked, but dimly.
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Satan
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Are the lenses the same?
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Cloggy Saint
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Lenses are the same and original. Sorted now, it was just the bulb. I always thought a bulb worked or it didn't, never realised they could partially work 
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Brianmoooore
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I've taken tail light bulbs out of various BMW models that are so blackened that they no longer emit any visible light, although they are still 'working'.
If your fog light bulb was blackened, it was probably a result of it being held with bare fingers when fitted.
If your fog light bulb was blackened, it was probably a result of it being held with bare fingers when fitted.