Rear fog light not working

[Dwuk2000]

Hi,

Van failed MOT today due to no rear fog light, was hoping it was an easy fix but doesn't seem so.

It's an 2017 ex-AA van with Genuine LED rears fitted, I've checked the cabling and as some say the Grey/White cable should be in slot 2 and others 5, have tested both. Checked the 15amp fuse and this was strangely missing so added one.

Will do a reset later as per Rear fog lights not operating [Resolved] and check the green connection under passenger seat.

I wondered if it's the tow bar electrics that were removed over a year ago, do tow bars need to be coded and if so does that coding need to be removed?

Cheers

 

[roadtripper]

Hi,

Van failed MOT today due to no rear fog light, was hoping it was an easy fix but doesn't seem so.

It's an 2017 ex-AA van with Genuine LED rears fitted, I've checked the cabling and as some say the Grey/White cable should be in slot 2 and others 5, have tested both. Checked the 15amp fuse and this was strangely missing so added one.

Will do a reset later as per Rear fog lights not operating [Resolved] and check the green connection under passenger seat.

I wondered if it's the tow bar electrics that were removed over a year ago, do tow bars need to be coded and if so does that coding need to be removed?

Cheers

Depends what kind of towbar was fitted.

If it was OE they tend to work with the canbus and disable foglights and rear sensors when trailer detected.

If it was a more basic one then traditionally the foglights would be wired through a switch in the towbar socket so that when the plug was in they disconnected. It seems less likely given I'd expect AA to use decent kit but might be worth checking for interruptions.

 

[dubber36]

Is the warning light on the dashboard coming on when the fog lights are turned on?

Are you getting power coming out of the rear foglight pin on the headlight switch when they are turned on?

My understanding with coding towbars is that the van will operate in a different way when the trailer is plugged in, but act normally with nothing plugged in. I wouldn't have thought it needed to be uncoded.

 

[Dwuk2000]

Cheers for the replies, I have a few things to test over the weekend, no signal on the Grey/White cable that I can see, so will dig deeper.

Has passed an MOT since the strip out so started with the lights.

 

[Dwuk2000]

Probably a stupid question but would there be any issue going from a headlight switch with single fog lights to one with two fog lights?

Have an aftermarket auto lights fitted that you pull out twice for rear fogs, where before I had the basic single:

 

[roadtripper]

Have you changed the switch since you last had successful foglights?

I can't imagine there would be a fundamental issue, but any change is an opportunity for something to be not in the right position or come loose?

I'd certainly try and check that you are getting voltage on the pin you are expecting to as @dubber36 suggested.

If you have the switch out and a multi meter the buzzer connectivity setting or low resistance setting you should be able to check the internal connections and find the foglight pin to compare with the wiring.

 

[dubber36]

My money is on the switch. I've had several failed aftermarket switches over the years in various different VWs. The switch supplied with the aftermarket auto light kit I bought for the Polo didn't last long before the headlights started doing strange things.

 

[DXX]

Plenty of genuine VW used switches on Ebay for 25-30 quid.