Solar sunroof intermittent now not working

[HPsauce]

My question is, where do I start on diagnosing and fixing it?
The ventilation fan works totally normally except the solar sunroof no longer activates it.
For quite a while it had been intermittent, sometimes working, sometimes not, suggesting an relay or loose wiring issue.

I know there's a lot of stuff on the A8parts forum that could/would guide me but it's never up these days!
Where's a good place to start, checking voltages etc.? Or even just swapping a relay?

[Fredde9912]

Here are some current flow diagrams assuming you have a multimeter it's just a case of tracing where the power stops flowing.

[Fredde9912]

Here are some current flow diagrams assuming you have a multimeter it's just a case of tracing where the power stops flowing.

I tried to attach the images but didn't work will try to send you a message.

[Edit]
Same issue when trying to upload the diagrams but maybe you can find them yourself on Elsa if you have access.

[HPsauce]

Thanks. Yes, I think I have Elsa somewhere, and I have the old Bentley manuals as well; I'll need to boot up a virtual XP system to get into them though!
Just thought someone might say - commonest problem is X, start here.

[HPsauce]

I know there's a lot of stuff on the A8parts forum that could/would guide me but it's never up these days!

PROGRESS! The A8parts forum is up (how long though?) so I dived in, found the relevant threads (including the one where IT did a full retrofit) and have downloaded the entire content of them, text and relevant images, to my PC.
Now I know which relay, where it is, the wiring layout, etc. So I'll be diving in when the weather is a bit cooler and the cabin isn't 50C or more (due to no solar fan... )
Incidentally I did raise this very question there (A8parts) a while back (2 years ago) when the problem was just intermittent and Sean pointed me in the right direction. But I never got round to it and forgot what he said then ....
FYI: The relay part number is 8A0951253A and is stamped with the number 203. It sits in position 7 in the relay plate in the passenger footwell.

Of course, Sod's law says I don't have a spare 203, though oddly I do have a couple of 204's! Ordered a used one off eBay.
I presume the 204s are from taking out the starter relay when I had F125 problems and put a bypass wire in there instead. It's probably still there, I don't recall bothering to replace it. Maybe I never will? Edit: I must have done, it only starts in P or N.

[HPsauce]

The mystery deepens....
Today I decided to go into the electronics box under the passengers feet, just to have an initial "recce". Photo attached.
Oddly I couldn't see the relevant relay in position 7 and reaching behind the small 219 relay at the front I could feel nothing!
Looking at the photo there's no evidence of a mounting plate for it or wiring to it either. Maybe the suspect one is there but has been moved?
I need to use the car this weekend so I'll leave well alone until the new relay arrives next week.
EDIT A little rummaging online suggests it may be in position 13 not 7 so I won't panic. 7 and 12 look empty, 13 has wiring.

FootwellRelays.jpeg

I was also intrigued by the black tape on the brown wire into the brown relay (389, wipers?) so took it off to reveal a stub of black-insulated wire twisted round a bared section of conductor, not soldered or crimped, just twisted on! Definitely nothing I'd done, so I removed it and taped over the very short bared section again. Presumably someone before me fitted an accessory of some sort - badly.

[HPsauce]

If I do get this working my next "project" may be to try and reinstate my "Solar panel inhibit switch" that MJ (very sensibly) removed a few years ago when working on the car.
The switch and some wiring are still there, my mistake was to put it in the full-power circuit between the solar panel and blower, not using components of adequate current capacity.

Now I know a bit more the hopefully obvious way to implement this is somewhere in relation to the relay, presumably in the trigger circuit from the HVAC system? Would it literally be as simple as just disconnecting that wire? Or does it work the other way round with the HVAC signal telling the relay to switch to the HVAC supply/control so the ignition-off default is solar?
The aim is to be able to turn off the solar power to the fan in cooler weather; I often used to find it blowing freezing air into the car on bright winter days.

[HPsauce]

The switch and some wiring are still there, my mistake was to put it in the full-power circuit between the solar panel and blower, not using components of adequate current capacity.

The more I look at this the more I'm convinced that my original method is the only relatively simple way that works.
Checking the 203 relay it's clearly a flip-flop between powering the blower from the car 12v supply or the solar panel, with the default being solar.
It's obvious really, even Audi wouldn't design a system that required a permanently-energised relay just in case the sun came out while parked!

So I'll look at using suitable wiring and switches for a circuit that in theory (but probably not in reality) could run at up to 40A/12V.
As before, the Earth side of the solar panel circuit seems the obvious place to tap in, it has connectors crying out to be used.

[HPsauce]

FYI: The relay part number is 8A0951253A and is stamped with the number 203. It sits in position 7 in the relay plate in the passenger footwell.

So that was correct, but only up to September 2000; Audi moved it to 13 from October! Sean found this:

RelaysETKA.png

What a J541 is I've no idea, I presumably don't have one as 7 is empty, as is 12 which is Servotronic that I also don't have.
J44 I presume is the A/C clutch and I know mine works fine.