Mk mk2 vRS just failed it's MOT on the side and tail lights. After looking at previous posts it sounded like it was an incorrect fail due to the side lights just being dummy lights but I no longer think that is the case.

 

When I first bought the car I fitted an automatic headlight switch that worked, apart from the fact that the interior lighting that turns on when the headlights are on no longer illuminated. The dashboard cluster also no longer illuminated brighter when the headlights were on but by the time I realised this was the case I was already used to it being dim...

 

When it failed I looked at how the auto headlight switch worked in more detail and I think there's an issue with the lighting, electrics or the ECU. Even when installing the original light switch there are still issues and I'm not sure what to do next.

 

Behaviour when original headlight switch is installed:

Off - No lights at all on, including DRL

Side lights - No lights on, including DRL

On - Dipped beam and dim DRL, no rear number plate lights

Lights on dashboard cluster: no dashboard lights show on any light setting

 

Behaviour when auto headlight switch is installed:

Off - Only DRL on

Side lights - No lights on

On/ Auto on - Dipped beam, dim DRL and rear number plate lights (this is what I understand is expected behaviour)

Lights on dashboard cluster: Only the headlight light shows when switched to On/ auto on

 

I've tried toggling the DRL switch by the fuse box but they then only came on dim with the dipped beam, nothing came on when switching to side lights.

 

I've ordered a couple replacement light switches that will arrive tomorrow to see if it's a switch issue. The current auto headlight switch is missing one connector meaning the 'plus connection in instrument panel' is not connected. However I'm not sure if it is a switch issue if the original switch works even worse than the cheap auto headlight switch.

 

Any advice would be greatly appreciated! At the moment I believe the issue resulting in a failed MOT is that on the side light setting there is no DRL and rear number plate light illuminated.

 

If the new switches don't work I'll ask the garage to start their diagnosis.

 

Thanks in advance!

Sorry i can not help with the fault.  I hope someone can. 

 

Best be clear what you have, 

What you are calling Dim DRL's are when the are Sidelight / Position lights at the front.  The same Unit is DRL when bright and go dim when they are te Sidelights.

 

When they are on as DRL's, (Bright)

 will be or should be when the Sidelights or Sidelights and Headlighrs are not on.

Edited 23 August, 20214 yr by e-Roottoot

2 hours ago, North97 said:

the interior lighting that turns on when the headlights are on no longer illuminated. The dashboard cluster also no longer illuminated brighter when the headlights were on

These actually sound like advantages to me!

2 hours ago, KenONeill said:

These actually sound like advantages to me!

Haha that's why I didn't swap back to the original switch! 

3 hours ago, e-Roottoot said:

Sorry i can not help with the fault.  I hope someone can. 

 

Best be clear what you have, 

What you are calling Dim DRL's are when the are Sidelight / Position lights at the front.  The same Unit is DRL when bright and go dim when they are te Sidelights.

 

When they are on as DRL's, (Bright)

 will be or should be when the Sidelights or Sidelights and Headlighrs are not on.

Thanks for the reply. Correct! The DRL lights do not come on in the dim state when turning on the side lights like expected, they're completely off.

 

They are only on when the switch is off (bright) and when they headlights are on dipped beam (dim).

 

I'm going to take it into a VW specialist and see if they can diagnose it as I think the auto headlights have effected the ECU, that's my guess. I regret putting in this cheap auto headlight switch now!

Interior light as far as I know, only comes on when at least the side lights are on. (May be different if drl's are on).

If you had an auto switch, the first click right, from the off (o) Position, should have set the auto lights which then only come on in the dark/dimly lit area and also in tunnels. The MOT guy may not have noticed that! If they have not light true to it being light, the interior dash lights, the numberplate ones, etc will not light either.

It takes the second click right, of the switch, to put sidelights n, then all should light up. The third click will put dipped beam on, along with the dipped beam light on the dash, which won't come on with just sidelights. Flick the left stalk to high, the beams go high and the blue light comes on too. 

It sounds strange that there is an issue with bOTH switches so was the original one faulty in the first place? Do you have a genuine auto switch or some sort of cheap copy? 

I have noticed on my VAG scan/code tool, there is a section regarding auto lights so wonder if your model required coding, in order to function correctly. This may be more likely if you have maxi dot as they tend to have more functions and if you have original VW switches as they may be more technical then cheap Chinese copies, that may be designed to "Plug and play" as often quoted. 

put the original switch back in  (throw the auto one on the bin)  and then check the fuses...................if that sorts the tail and number plate lights, don't worry the about ones in headlights, they do not work from the factory, the tester needs to have it explained "assuming" your DRL's come back on and work in the sidelight position as well