Fog Lights Not Working
Discussion
Hi this is my first post so do be kind 
I have a '91 Polo Coupe and the fog-lights aren't working.
The story is a bit complicated because when I bought the car 2ish years ago there was no switch for fogs on the dashboard so I assumed the car had never had fog lights fitted.
I thought this because the trim spec for Polo Fox is so mean but I now know I was wrong
So recently I've done some investigations to see what is in place.
Looking under the dashboard and behind the switch/radio/heater part of the facia there was:
> No socket for Fog Light Switch to connect to.
> No Wiring Loom for the Fog Light Switch/Socket assembly to connect to.
> Number 21 Relay was in place (which I've been told is the relay for foglights as well as the indicators.)
> A Yellow & White wire leading from the No 21 Relay towards the Rear Light Cluster and forwards to the Front Fog Light connector in the Engine's Plenum Chamber.
I also looked in the rear light assembly and saw abulb in the chamber for Fog-Lights.
So as far as I know the car was missing only the wiring loom and the Fog Light Switch to restore function to the car.
So I've acquired both the section of loom and the switch and installed both.
BUT unfortunately the Fog Light still refuses to work!
> I've cleaned all the contacts in the switch and socket.
> I've checked the fuse which is fine.
> I've changed the Number 21 Relay.
Still no joy is there something else I should try to get the fog lights working?
I'm guessing this must be something related to why the Loom & Switch were very thoroughly removed way back in the mists of time but I'm thinking that sooner or later it will catch me out on the NCT, although so far its gone through 2 without a word said.
I have a '91 Polo Coupe and the fog-lights aren't working.
The story is a bit complicated because when I bought the car 2ish years ago there was no switch for fogs on the dashboard so I assumed the car had never had fog lights fitted.
I thought this because the trim spec for Polo Fox is so mean but I now know I was wrong
So recently I've done some investigations to see what is in place.
Looking under the dashboard and behind the switch/radio/heater part of the facia there was:
> No socket for Fog Light Switch to connect to.
> No Wiring Loom for the Fog Light Switch/Socket assembly to connect to.
> Number 21 Relay was in place (which I've been told is the relay for foglights as well as the indicators.)
> A Yellow & White wire leading from the No 21 Relay towards the Rear Light Cluster and forwards to the Front Fog Light connector in the Engine's Plenum Chamber.
I also looked in the rear light assembly and saw abulb in the chamber for Fog-Lights.
So as far as I know the car was missing only the wiring loom and the Fog Light Switch to restore function to the car.
So I've acquired both the section of loom and the switch and installed both.
BUT unfortunately the Fog Light still refuses to work!
> I've cleaned all the contacts in the switch and socket.
> I've checked the fuse which is fine.
> I've changed the Number 21 Relay.
Still no joy is there something else I should try to get the fog lights working?
I'm guessing this must be something related to why the Loom & Switch were very thoroughly removed way back in the mists of time but I'm thinking that sooner or later it will catch me out on the NCT, although so far its gone through 2 without a word said.
Presumably NCT is the equivalent of the UK MOT? - annual safety check at a test station.
Is rear fog light required? It is for MOT but no idea for NCT.
Slightly silly question - when you tried it did you have front headlights or fog lights turned on - normally you can't have rear fogs on without something more than sidelights at the front.
If it isn't that then work your way through each connection/switch and see if there's power at each step. Either use a multi meter or a bulb on a wire, may have to think up a probe to poke into connectors to do it - bit of wire, nail etc then wire to the test bulb and from there to earth.
Using the same relay for indicators and fogs seems a little odd??
Is rear fog light required? It is for MOT but no idea for NCT.
Slightly silly question - when you tried it did you have front headlights or fog lights turned on - normally you can't have rear fogs on without something more than sidelights at the front.
If it isn't that then work your way through each connection/switch and see if there's power at each step. Either use a multi meter or a bulb on a wire, may have to think up a probe to poke into connectors to do it - bit of wire, nail etc then wire to the test bulb and from there to earth.
Using the same relay for indicators and fogs seems a little odd??
Check the bulbs are working!
Use a multimeter to see if there is 12v to the bulb holder.
You may find that the fog light will not come on if the car's headlights are not on dipped beam. I say dipped beam as I am aware of at least one vehicle that automatically switches off the rear fog light when you go to main beam.
The car might be a bit too old, but if lights etc are controlled through an ECU or BECM then it may need to be programmed so it knows the light is there before it will work.
Use a multimeter to see if there is 12v to the bulb holder.
You may find that the fog light will not come on if the car's headlights are not on dipped beam. I say dipped beam as I am aware of at least one vehicle that automatically switches off the rear fog light when you go to main beam.
The car might be a bit too old, but if lights etc are controlled through an ECU or BECM then it may need to be programmed so it knows the light is there before it will work.
Edited by paintman on Wednesday 27th November 19:51
Are we talking front or rear fog-lights?
If it's just the rear bear in mind that there is only one rear fog-light on the driver's side (right side). The other is not connected even if there is a bulb in place. Apparently some countries allow only one rear fog-light so that it will not be confused with the brake-lights. So you need to check the rear right.
If it's front fog-lights come back and confirm.
If it's just the rear bear in mind that there is only one rear fog-light on the driver's side (right side). The other is not connected even if there is a bulb in place. Apparently some countries allow only one rear fog-light so that it will not be confused with the brake-lights. So you need to check the rear right.
If it's front fog-lights come back and confirm.
Hello
If you are still having trouble -
Trace the fault step by step in this below order
1) With Ignition switched on Black/Yellow should become live at the Side/Headlight Switch
2) With the Side/Headlight Switch in the Headlight's on position the Grey/Yellow wire at the Side/Headlight Switch should become live
3) Fuse number 2 should now be live as it is supplied from the Grey/Yellow wire mentioned in step 2
4) The output from Fuse number 2 is a Grey/Yellow wire that runs directly to the Rear Foglight Switch and should now be live if the fuse and box are ok
5) With the Rear Foglight Switch in the on position the Grey/White wire at the Rear Foglight Switch should now be live
6) The Grey/White wire at the Rear Foglight Connector should now be live and if the bulb and holder are ok the Rear Foglight will be working
There is a very good chance that some of your polo's switch panel wiring harness has been damaged and removed, many German vehicle harnesses have been burnt due to people fitting extras and using a black ignition feed or grey/blue illumination cable as the return (earth)
If you are still having trouble -
Trace the fault step by step in this below order
1) With Ignition switched on Black/Yellow should become live at the Side/Headlight Switch
2) With the Side/Headlight Switch in the Headlight's on position the Grey/Yellow wire at the Side/Headlight Switch should become live
3) Fuse number 2 should now be live as it is supplied from the Grey/Yellow wire mentioned in step 2
4) The output from Fuse number 2 is a Grey/Yellow wire that runs directly to the Rear Foglight Switch and should now be live if the fuse and box are ok
5) With the Rear Foglight Switch in the on position the Grey/White wire at the Rear Foglight Switch should now be live
6) The Grey/White wire at the Rear Foglight Connector should now be live and if the bulb and holder are ok the Rear Foglight will be working
There is a very good chance that some of your polo's switch panel wiring harness has been damaged and removed, many German vehicle harnesses have been burnt due to people fitting extras and using a black ignition feed or grey/blue illumination cable as the return (earth)
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