Dashboard Lights Don't Turn On With Light Switch

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JackCisco
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Dashboard Lights Don't Turn On With Light Switch

Post by JackCisco »

Hi,

I've got a pretty annoying issue with my dashboard lights on my 2011 Polo.

Now I know they definitely work, because during the day the light sensor in the speedo gauge makes them light up and when it gets dark they go out.
The issue is that they don't come on along with all the other dash lights when I turn the light switch to sidelights or headlights.

As a result it has failed MOT because even though it has a 2nd speedo in the screen in the middle which I've used for driving the past 3 years the test station was adamant that the gauge had to light up as well.

What I've tried to rectify this so far:
Checked all fuses
Replaced light switch
Replaced dimmer/headlamp level switch
Replaced interior power delivery control cluster ECU thing (big plastic box that has 2 large connectors going into it with tonnes of cables)
Replaced the gauge cluster
Jumped pins on the dimmer/headlamp level switch from brown cable to slate/blue cable

Nothing has worked, I'm confused as hell as to what this could be and I don't have a wiring diagram for any of this, even in my Haynes manual so I'm literally just guessing at this point.
It would make a bit more sense if the gauge cluster lights didn't work at all but they do..

If you need specifics my Polo is a 1.2L 3 cylinder super duper basic trim.

Any help is greatly appreciated. Please ask if you need more information. I haven't driven this thing for over 3 months it's about time I get it back on the road!!
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iichel
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by iichel »

are all the other buttons illuminated in red?
JackCisco
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by JackCisco »

iichel wrote: Wed Jun 23, 2021 9:10 am are all the other buttons illuminated in red?
Nope nothing else lights up on the dash. I'm sure there are lights on the dimmer/headlight level switch too which don't light up.

The headlight switch does light up itself when in DRL/off mode or headlight mode.
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iichel
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by iichel »

I'd really recommend to check the fuse again, because this should really blow a fuse:
Jumped pins on the dimmer/headlamp level switch from brown cable to slate/blue cable
Try bridging the yellow/black cable to the grey/blue cable on the dimmer switch.
JackCisco
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by JackCisco »

iichel wrote: Wed Jun 23, 2021 5:32 pm I'd really recommend to check the fuse again, because this should really blow a fuse:
Jumped pins on the dimmer/headlamp level switch from brown cable to slate/blue cable
Try bridging the yellow/black cable to the grey/blue cable on the dimmer switch.
Thanks for the suggestions. I double check all fuses and if they're all good I will then see what happens jumping the two cables you suggested. I'll try it this evening and report back.
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by JackCisco »

iichel wrote: Wed Jun 23, 2021 5:32 pm I'd really recommend to check the fuse again, because this should really blow a fuse:
Jumped pins on the dimmer/headlamp level switch from brown cable to slate/blue cable
Try bridging the yellow/black cable to the grey/blue cable on the dimmer switch.
Ok so I checked all the fuses first, all of them absolutely fine.

I then jumped yellow/black to grey/blue at the dimmer switch connector and it sparked for a sec then blew this fuse:
Image

Sure I saw one of the lights in the gauge cluster go out, battery light maybe? But essentially there is no change to the current state of things aside the fuse now.

Any thoughts?
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iichel
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by iichel »

Fuse 11 is the fuse that powers the yellow and black wire to the dimmer.
So it seems you're having a short circuit in your 58d (dash illumination) circuit somewhere. Either in the wiring, a coupling point (like the door connector) or in a light/button/switch.
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by amer6R »

If you are having a short, maybe If you have VCDS it could help you to pin point the issue faster. ( To specific part)
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by JackCisco »

iichel wrote: Thu Jun 24, 2021 8:24 am Fuse 11 is the fuse that powers the yellow and black wire to the dimmer.
So it seems you're having a short circuit in your 58d (dash illumination) circuit somewhere. Either in the wiring, a coupling point (like the door connector) or in a light/button/switch.
So what makes you think that now?
Is there a wiring diagram available anywhere that includes this circuit?


amer6R wrote: Thu Jun 24, 2021 8:28 am If you are having a short, maybe If you have VCDS it could help you to pin point the issue faster. ( To specific part)
Unfortunately I don't have access to VCDS :(
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iichel
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by iichel »

I don't think this car has a diagnostic connection on the 58d circuit.

There might be an issue with the light switch, which i doubt.

The path is: light switch -> SB7 -> dimmer T6/3 in -> T6/5 out -> the rest of the car.
So your best call is to check fuse 7, the input of pin 3 of the dimmer and the output pin 6 of the dimmer.
Check for voltage on the input and output sides of the dimmer. If these are OK, the fuse is fine. And check resistance to GND.
If there is a short to GND somewhere (which is likely due to the fuse 11 blowing), you need to find it.
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by JackCisco »

iichel wrote: Thu Jun 24, 2021 12:05 pm I don't think this car has a diagnostic connection on the 58d circuit.

There might be an issue with the light switch, which i doubt.

The path is: light switch -> SB7 -> dimmer T6/3 in -> T6/5 out -> the rest of the car.
So your best call is to check fuse 7, the input of pin 3 of the dimmer and the output pin 6 of the dimmer.
Check for voltage on the input and output sides of the dimmer. If these are OK, the fuse is fine. And check resistance to GND.
If there is a short to GND somewhere (which is likely due to the fuse 11 blowing), you need to find it.
Ok I'll check it out and see what I find.

What do you think of this:
The little micro chip on the PCB of the dimmer switch gets extremely hot. Touching the chip itself burns my finger in about a second and the heat warms the plastic casing a fair bit. It has been doing this before I posted here.
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iichel
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by iichel »

makes sense since it has a high load on it, if my short circuit theory is correct.
you said you replaced the dimmer, did both dimmers show this heat up?
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by JackCisco »

iichel wrote: Thu Jun 24, 2021 4:16 pm makes sense since it has a high load on it, if my short circuit theory is correct.
you said you replaced the dimmer, did both dimmers show this heat up?
They both did yep. Making it seem like your short circuit theory is correct even more.

I'm guessing when I jumped those two wires it allowed enough current to pass through where the dimmer was just using it all up as heat.
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by JackCisco »

iichel wrote: Thu Jun 24, 2021 12:05 pm I don't think this car has a diagnostic connection on the 58d circuit.

There might be an issue with the light switch, which i doubt.

The path is: light switch -> SB7 -> dimmer T6/3 in -> T6/5 out -> the rest of the car.
So your best call is to check fuse 7, the input of pin 3 of the dimmer and the output pin 6 of the dimmer.
Check for voltage on the input and output sides of the dimmer. If these are OK, the fuse is fine. And check resistance to GND.
If there is a short to GND somewhere (which is likely due to the fuse 11 blowing), you need to find it.
Ok so checked fuse 7 again, definitely good.

Checked input pin 3 of the dimmer and got 12v there.

Went to check output pin 6 and it doesn't have that pin.

That connector for me is as follows (with headlight switch on sidelights):
Pin 1 - Brown cable, 1.6mV, 6.7Ω resistance to ground
Pin 2 - Red/blue cable, 2.4V, no ground
Pin 3 - Grey/yellow cable, 11.77V, no ground
Pin 4 - Black/yellow cable, 11.77V, no ground
Pin 5 - Grey/blue cable, 0.3mV, 1.9Ω resistance to ground
Pin 6 - Empty

So I have two grounded cables there, brown should be a common ground right? And grey/blue shouldn't be grounded?

The grey/blue goes off to the light switch, the interior control box, somewhere down the right side of the vehicle, somewhere across the dash to the left side of the vehicle (left and right number plate lights?), and to the hazard traction control and rear heater switches.

Both number plate lights work. I checked resistance on the grey/blue cable for them both at their connectors and resistance is below 1Ω.

The grey/yellow goes off to the light switch, the dash gauge cluster and then to what looks like an inline capacitor which then changes to grey/blue cable which goes back into the light switch and into fuse 7.

Do you have a diagram somewhere you're referencing?

(Edited to provide readings on each pin)
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iichel
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Re: Dashboard Lights Don't Turn On With Light Switch

Post by iichel »

I sent you the diagram via PB.

My next suggestion would be to remove the components on the 58d lines systematically and see if the illumination returns.
- disconnect BCM
- disconnect door wiring loom connectors in A/B pillars
- disconnect 12V socket plug
- disconnect other illuminated buttons in centre console like the heated rear window button
- disconnect light switch

everytime you connect a lighting source, with ignition off, you can turn the light switch to the parking light position to see if the other lights return
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