Rear fog light

the1andonly · Post by **the1andonly** » Sun Sep 13, 2015 5:42 pm

Have previously removed the red box hanging down off bumper and rewired the RHS reverse light to do this job (red bulb) passed last years MOT no probs.
Getting ready for next MOT checking lights Fog light doesnt work
change bulb no change
both bulbs light up when 12v appled direct from battery
DVM says 12V at socket when correct switches on
even tried a 3rd clear bulb no joy.
no corrosion evident
rear button moves in and out when replacing bulb.
Whats going on?

currently refitted / rewired the old red box, it works so will pass MOT
Whats going on?
is there a readily available light socket eg alternative model

cmm303 · Post by **cmm303** » Sun Sep 13, 2015 7:49 pm

Faulty earth?

the1andonly · Post by **the1andonly** » Mon Sep 14, 2015 8:06 pm

cmm303 wrote:Faulty earth?

Just added solder to bulb and ran separate earth wire, still doesn't work
12v on multi-meter.
confused still.

Post by **Simon Jones** » Mon Sep 14, 2015 8:13 pm

Assume you had side lights switched on at the time you tried the fog light?

teenmal · Post by **teenmal** » Mon Sep 14, 2015 8:42 pm

Simon Jones wrote:Assume you had side lights switched on at the time you tried the fog light?

I think they are using the reversing light assy,and 12v is present on the bulb holder contact when the switch is on.

Fassi · Post by **Fassi** » Mon Sep 14, 2015 8:51 pm

bulb loose in the holder?

Tony x · Post by **Tony x** » Mon Sep 14, 2015 8:56 pm

Problems like this can distroy your brain.
To be clear, there is 12 volts at the bulb holder, the earth is ok and the bulb is ok but it doesn't light up?

If you were to ask an electrician what was going on then they'd probably say that there isn't enough current to power the bulb as that's the most obvious explanation but even that appears unlikely. Another unlikely explanation is that, with a bulb in place, there is a short circuit. Still, as Sherlock Homes said, once you've dismissed the impossible, whatevers left, however unlikely, must be true

You could check it my measuring the voltage across the bulb with the bulb in place. Does it glow very dimly?

Often with such problems, it's easier to just rewire - You could connect wires from your old 'red box' to the reversing light fog light.

I recall an electrical problem on our Bongo that had me baffled for a while. It turned out the 12v supply I was using went to zero volts when the starter motor was engaged.

rita · Post by **rita** » Mon Sep 14, 2015 8:58 pm

Had same problem several times on various vehicles ,changed the bulb holders to cure it.

Post by **Simon Jones** » Mon Sep 14, 2015 9:19 pm

teenmal wrote:
Simon Jones wrote:Assume you had side lights switched on at the time you tried the fog light?

I think they are using the reversing light assy,and 12v is present on the bulb holder contact when the switch is on.

Yes, but if you get 12v on both contacts then it won't light up. Depending on how it has been wired, the fog light switch might be supposed to make the earth when it is in the 'on' position.

the1andonly · Post by **the1andonly** » Mon Sep 14, 2015 9:24 pm

[quote="Tony x"]Problems like this can distroy your brain.
To be clear, there is 12 volts at the bulb holder, the earth is ok and the bulb is ok but it doesn't light up?

Another unlikely explanation is that, with a bulb in place, there is a short circuit.

First statement 12v, even ran a separate earth, 3 working bulbs tried. no light
if there was a short circuit with the bulb in it then that would take out the bulb in red box (running off the same supply and earth.
The working red box indicates all switches work and in in correct position
same with and without engine running.

Rita
not surprised
from my original post
is there a readily available light socket eg alternative model

eg from mx5 etc from factors or has it to be a bongo scrapper?

rita · Post by **rita** » Mon Sep 14, 2015 9:32 pm

As a make sure test you could use the RL bulb holder from the n/s unit.

the1andonly · Post by **the1andonly** » Mon Sep 14, 2015 9:34 pm

Simon Jones wrote:
teenmal wrote:
Simon Jones wrote:Assume you had side lights switched on at the time you tried the fog light?

I think they are using the reversing light assy,and 12v is present on the bulb holder contact when the switch is on.
Yes, but if you get 12v on both contacts then it won't light up. Depending on how it has been wired, the fog light switch might be supposed to make the earth when it is in the 'on' position.

12v is between inner and outer of bulb holder
with all switches correct

the1andonly · Post by **the1andonly** » Mon Sep 14, 2015 9:37 pm

rita wrote:As a make sure test you could use the RL bulb holder from the n/s unit.

tomorows job
thank you.
tommorrows question will be
where can i get one

rita · Post by **rita** » Mon Sep 14, 2015 10:38 pm

You might be able to make something out of this lot.

http://www.ebay.co.uk/bhp/car-bulb-holder

the1andonly · Post by **the1andonly** » Mon Sep 14, 2015 11:51 pm

Sorry Rita
will read that tomorrow
well was tomorrow's question
But you have been known as mystic Rita in the past (problem with non standard valve stems)

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