Rear Fog Light continually on ?

[ChambL01]

Hi ,

(Micra K12, 57 plate 1.4 petrol)
The rear fog light bulb is continually on. At first i thought it wasn't working, but when i investigated found there was no bulb in the holder. On replacing a new bulb, the light immediately came on even with the ignition off and realized I had to remove the bulb too. I bought a new steering column indicator/ wiper arm suspecting this may likely be the issue, but it wasn't. I've also swapped the rear light cluster panel to exclude the drivers side being faulty, but the problem remains. Has anyone experienced this and found the cause.

Thank you

 

[MattInARedMicra]

I'm not sure what the MOT requirements are but I know it's illegal to drive with your fog light on if there is no fog, which explains why the bulb was removed so the car can be driven. It might be that it will pass an MOT with no fog light as long as the brake lights still work.

As for the remedy to the issue, I'd suspect that if it's always on even without the key in the car then you have a short circuit somewhere. With some components the only way to find out that they're draining power is to use a multimeter to identify the amp drain on the negative side of the battery and then test which circuit is active but with a bulb it's a bit more simple since you can see where your power is going.

I'd start by looking underneath the fuse/relay holders in the engine bay and checking for debris and rust or just a loose connection and go from there. Maybe clean the terminals up a bit and spray some wd40 (disconnect the battery first because it's flammable).

There's also a possibility that the fog light on this car is the "always live" type where the earth is switched. Which could point to an earth fault. The earth fault could be near the fog light where it is shorted and 'borrowing earth' from the other bulbs/wires or corrosion/debris is earthing the bulb onto the bodywork. If you're unlucky the earth fault could be anywhere along the length of the wire if there is a crushed wire or a split in the insulation.

Last possibility I can think of is damp has gotten into the relay or the relay just isn't working but has failed in the energised position.

good luck

 

[ChambL01]

I'm not sure what the MOT requirements are but I know it's illegal to drive with your fog light on if there is no fog, which explains why the bulb was removed so the car can be driven. It might be that it will pass an MOT with no fog light as long as the brake lights still work.

As for the remedy to the issue, I'd suspect that if it's always on even without the key in the car then you have a short circuit somewhere. With some components the only way to find out that they're draining power is to use a multimeter to identify the amp drain on the negative side of the battery and then test which circuit is active but with a bulb it's a bit more simple since you can see where your power is going.

I'd start by looking underneath the fuse/relay holders in the engine bay and checking for debris and rust or just a loose connection and go from there. Maybe clean the terminals up a bit and spray some wd40 (disconnect the battery first because it's flammable).

There's also a possibility that the fog light on this car is the "always live" type where the earth is switched. Which could point to an earth fault. The earth fault could be near the fog light where it is shorted and 'borrowing earth' from the other bulbs/wires or corrosion/debris is earthing the bulb onto the bodywork. If you're unlucky the earth fault could be anywhere along the length of the wire if there is a crushed wire or a split in the insulation.

Last possibility I can think of is damp has gotten into the relay or the relay just isn't working but has failed in the energised position.

good luck

Thank you so much for this. Ill be looking more at this tomorrow with your suggestions. This is a great help, Thank you