Cabrio roof problem (electrical)

[An o' Neamus]

Hi,

Just bought a 2000 model Golf Mk4 (3.5) Cabrio. I've posted this in the Mk4 forum, but am doing it here as well as the car is (in respect to the roof) identical to the Mk3.

Everything was working well until I had an aftermarket stereo fitted. The fitter had some problems getting the stereo to switch on/off correctly with the ignition key and finally resorted to an 'always on' solution.

During the fitting I think he must have shorted something, as now the electric roof won't operate at all (no clicks, whirrs or anything) when pressing the roof button. There are no fuses blown, so I'd imagine something has gone wrong with the circuit that tells the roof mechanism it's "ok" to allow the roof to operate (ie. ignition is switched off). All other electrics seem to work OK, so it's probably not the X reduction relay (18).

I'll probably take it into a VW dealership to have it looked at, but I'm a bit nervous as here (in South Africa), noone has much experience with the Cabrio.

Does anyone here know how to bypass the roof cutoff (ie. allow the roof to be operated while the engine is running)? Or can give me some clues to give to the VW mechanic so that he can find the problem without it costing me 1000s and having him dismantle the entire electrical system?

Thanks in advance!

PS. If it helps, at some point I think he may have joined the live 12v to the "brown and red" ignition switch line...

[Crasher]

The power to the roof switch comes from the S terminal of the ignition switch which is live with the key in but turned off. This supply also goes to the radio at socket 4 of the radio power plug as a brown/red wire. If you remove the roof switch, you should have power at socket 3 (brown/red) of the plug with the key in but off.

[An o' Neamus]

Thanks, there is no power on the brown/red wire at any time... Which I guess is the cause of the roof problem...

During the fitting of the stereo, the fitter joined the brown/red wire at pin 4 to the live 12v at pin 1 or 2, which may have shorted something. He also may have put too much load on the brown/red wire by connecting the 12v in of the stereo to pin 4, which could have blown a fuse, but I can't find it...

[Crasher]

You can’t find a fuse for the brown/red as it doesn’t have one, he may have damaged the ignition switch which is a pain to change. There is a connector behind the fuse box where the single 1.0-mm red/brown from the switch splits off to the roof switch and to the radio, this may be disconnected.

[An o' Neamus]

Thanks for your quick replies!

Is there any way to test for a faulty ignition switch (to avoid replacing it when it's not the problem)? Or hardwire the brown/red so that it is always "on", even when the key is not in the ignition (or the ignition is not in the S position)?

I've done a continuity test on the brown/red wire from the ignition switch plug to the radio plug, and found no break. I'll do the same on the roof switch wire. Although I suspect the result will be similar (roof mechanism is not faulty AFAIK). So, although there is an electrical connection between the red/brown wire on the radio plug and the red/brown wire on the ignition switch, there is no current on that wire at any time.

[Crasher]

The switch has a very big power feed cable so that will be OK. You could drop the lower column cowl off, unplug the switch and then check the continuity (using a multimeter) from the S socket to the roof switch. You MUST NOT hot wire the plug, it is a safety lockout to prevent the roof being operated when moving.

[An o' Neamus]

Thanks, will do. Any tips on removing the roof switch? Does it just pull out?

I understand the safety issues of operating the roof whilst the car is moving, and wouldn't do that. I'd be interested in hotwiring the roof to isolate this issue. Also if that fixes this problem, I wouldn't mind being able to raise/lower the roof when the car is idling...

[An o' Neamus]

Crasher, thanks for all your help! Turns out it is the ignition switch. I did the continuity tests etc. and found no breaks in the wiring (as expected) and no 12v on any key position (the problem)...

If I press the key in hard and try to turn it the wrong direction and hold it there, then the roof circuit becomes active. So it must be the ignition switch.

I am tempted to take a wire from the 12v on the cigarette lighter socket to the roof switch and leave it like that (I don't really understand the safety issue, as you'd have to release the roof catches first anyway, and that alone would probably destroy the roof if you were moving). But I feel a lot more comfortable taking it to the dealership and saying "please replace the ignition switch" rather than "please find the electrical problem with the roof".

How difficult is it to self fit an ignition switch?

TIA

[Crasher]

The switch has lost its “S” position so a new switch will fix it. Unfortunately they are a complete pain in the bottom to do. First of all the air bag has to be removed (disconnect the battery first, do not have the ignition on with the air bag disconnected or a trip to someone with a diagnostic machine will be required). Then the steering wheel adapter sleeve has to be extracted from the column shaft which is very difficult to do without a special puller. After that, it is easy to slide off the column lock unit and the switch is held in by a small cross head screw. Some people remove the whole assembly from the car to avoid removing the sleeve but as I have a puller, I have never done this.

[An o' Neamus]

Thanks, that looks way too complicated and far too easy to create additional problems, so I'll get it done at a dealership at some point (gonna have to extract the repair bill from the radio installer - I already made them refund the installation charges)... The installer must have connected the red/brown wire to earth while the key was in the ignition and shorted the 'S' switch position in the ignition switch.

For now, I've joined the red and red/brown wires on the radio plug. From the schematics that I have, it appears as if this wire only has end points on the radio plug, roof switch and ignition switch (with a splitter terminal behind the relay plate).

The roof works now (all the time!)... Anyone know what VW's safety concerns (regarding not allowing the roof to be operated whilst the engine is running) are?