None of the lights inside the car is working

[yaman]

All of the connections in the undercarpet harness are sound and tested. is there anything else I can do?

There's also an under-carpet loom in the rear near/side foot-well
that has corroding joints, and needs to be checked as-well.

Regards
Jim

[JohnPierpoint]

Similar problem on my 03 Passat. The Haynes manual shows that all the lights are controlled by the "convenience system control unit". This is the same unit that controls the alarm, and that's been giving me grief on and off for months now too (although just lately it's stopped going off, but I suspect it's not working at all now. . .). Unfortunately - according to the Haynes manual again - access to this unit involves removing the front passenger seat, disabling the airbags, inserting a custom adaptor to prevent the side airbag from going off. . . VW sure know how to make life hard for us!
I notice that several postings in this thread talk about just pulling up the passenger-side carpet (without all that palaver of removing the front seat and airbag), but from past experience with VWs, I'm reluctant to start removing anything until I know how to do it properly. Usually the outcome is a broken bit of plastic and a part that will never refit. (This has just happened with the vanity mirror light housing, and it doesn't get any simpler than this part!)
Can anyone direct me to any other threads or sites that cover this procedure? Or is it easy to do in this case?
I suppose I really ought to take the thing to a garage to have it properly looked at, but my usual mechanic won't touch the alarm system. Does anyone know of a good place near Birmingham that can tackle the repair or replacement of the control unit?

Thanks to everyone who has posted in this thread - very informative!

[Crasher]

Haynes comic! Remove the left kick panel trim, unclip the sill edge trim, lift up the carpet/sound deadening (very heavy and thick) and the convenience system is under there in a black box and it will probably be swimming in rain water.

[JohnPierpoint]

Thanks for the speedy reply, Crasher. I'll give it a try in the morning.
I don't know why I bother with Haynes manuals after all these years, but I still always get one and carry it in the car "just in case". I suppose these days it's far better to just get "real world" info from fellow owners and professionals on the web. Is there another publisher that does better (paper) 3rd party manuals?

[Crasher]

A decent paper manual would be so big it would fill 3 volumes.

[JohnPierpoint]

Here's an update to my own problem: I checked under the carpet way back when I made my last posting, but everything seemed OK. It was a little damp, but not soaking, and all the wires I could see were OK. Being a bit timid about damaging the car further, I left it at that for the time being. Since then, other electrical problems started to occur: the low oil warning came on (checked out during a service – plenty of oil); the central locking became erratic; the electric windows failed. Finally the fuel cap release failed (and on this model, there seems to be no manual override), and we realised that we couldn’t put it off any longer. So we started checking again. This time, I was a little less timid in pulling up the carpet, exposing more of the loom and the CCM. There was a lot more water this time. We used the excellent how-to article at http://www.veedoubleu.com/?page_id=4 to remove the battery and clear the drain holes. (Unbelievable: I had to take the bloody windscreen wipers off just to lift out the battery!). Meanwhile the under-carpet area got the hair-dryer treatment. I checked all the exposed wires and joints, but they still seemed to be OK. When the battery was replaced, the oil warning, locking, windows and fuel cap problems had gone, but still no interior lights. Tomorrow, we will continue to dry out the under-carpet area (maybe a drive around with the AC at high temperature!) and possibly extract the CCM. Some articles say this is loose under the carpet, but ours seems to be held by an inaccessible clip somewhere.

[Crasher]

Give the junction of red/black wires a good pull from both sides, if it comes apart that was the problem.

[JohnPierpoint]

Update: after yesterday's drying, everything worked fine this morning!
But after driving a short distance, things started going wrong again: no locking, no fuel cap, etc. . .
Then when we came to work on it again, the alarm decided to go off (after not working for several months). No way to shut it off. Even removing fuse 14 didn't stop it this time.
There was a lot of water again around the CCM and loom. Maybe this was already under the carpet, and had just moved due to the car being driven (it's parked on a slope).
The CCM has now been extracted. The contacts on one connector block were clean, but the other block was full of verdigris and water.
This is now being cleaned, and the loom is being dried off again.

We were considering moving the CCM by extending the wires, and then positioning it say under the passenger seat or partway up the passenger footwell or inside the glove box. Has anyone tried this?

The plastic trim under the wipers now doesn't sit flat against the window (not that it ever did, but it's worse than before), so I wonder if water can be going down the back of this and finding another route down under the carpet. I was considering filling this gap with something that would stop the water, but not prevent me from lifting the plastic trim when I come to replace it. Some soft non-setting mastic is called for. Has anyone tried doing this and can recommend a good filler?

[Paulst]

If you have cleaned out the drain holes then it's possible that the foam seal arround the Pollen Filter Housing has started to fail.

[JohnPierpoint]

This is odd, because I've seen several mentions of the pollen filter seal with regard to water ingress, yet my own car seems to have no seal around, over or under the pollen filter. The filter itself doesn't look capable of stopping much water, as it is a paper type. It sits in a rectangular frame, with only a small plastic clip holding it down lightly on one side. I wonder if it's missing a cover or something?
Does anyone have a photo of how the pollen filter housing should look?

The good news is that I can't see any evidence of water under or around the filter.

Update: CCM contacts now cleaned up, apart from pin 21 on the 23-pin block, where the female contact on the wired block has corroded and broken. This appears to be the switch for the interior lights, and as I haven't had these working for quite a while, I reckon I can live without them for a little longer until I can rig up something. I don't hold out much hope of extracting the remnants of the corroded contact from the block, which means I can't just buy another contact and slot it in. However, I think I can solder a wire onto the CCM board and bypass the connector block with a suitable inline connector. Once this is done, the CCM is going to live on top of the carpet for a while until I'm sure it's all working OK.