I’ve got a MK3.5 Roadster and can’t get the interior light to work when opening the drivers door. The bulb is ok because the light works when you open the passenger door and it also works when the unit is switched to the permanently on position. Any fuses for this circuit must presumably therefore be ok and the lamp unit itself must be also? I’ve tried swapping the door switches around but the problem is just the same. Does anyone have any ideas please? I’ve tried doing a search and it seems a few people have had similar problems but I can’t seem to find a definitive solution? Cheers
Sounds like the wire to the door switch is faulty if a new switch hasn’t sorted it.
Yep. It’s difficult to see what else it could be. B!tch to fix: especially as it’s a minor inconvenience unless you love fixing electrical issues.?
Agreed. Most likely in the door hinge area where the loom goes from the door into the pillar. Or the door has been apart and the loom has been incorrectly routed allowing a wire to get caught by the window mechanism etc. Try identifying the wire and testing for continuity with an ohmeter.
Thanks everyone for your replies, unfortunately you’ve just confirmed my fears that it’s likely a wiring fault somewhere which will no doubt be a PITA to find/trace! 
I’m talking rubbish as the wire isn’t inside the door, its running inside the car! 
I think that it’ll be a fault with the instrument cluster from my experience.
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That’s upset the applecart😀 …. what’s the thinking behind this?
Why do you say that, how would they be connected? 
From memory I seem to recall the circuitry runs though the IC for the door open warning light and I think that a component (diode?) fails. If you post your VIN I can give you some tests to carry out but I won’t be able to do so for a week or so as I’m going away.
Have you seen this topic and the one I’ve linked to in it?
When I had my interior stripped out - i took this picture.
There is only one wire coming from the switch directly in to the loom.
@CBRDEANO I think that wiring diagram simplifies the circuit somewhat, there’s a lot more going on inside the IC.
Looking at the wiring diagram again now, I think that it’s the lower of the 2 diodes under DOOR (LED) that fails.
@SteveMK3 Bridging the Blue/Black (L/B) and Black/Blue (B/L) wires in connector C-11 or at the connector on the back of the IC with a bent paperclip will probably get it working, if you’re keen I’ll point you towards C-11, but try this at your own risk.
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Thanks everyone but sadly I think this is going to be something I just have to live with and ignore as it looks like it could get too complicated unfortunately!
I had the same problem on a NC 3.75 and led another earth from the lamp holder to the door switch which cured it.
Obviously you have to remove the header rail, A post cover and sill cover.
Thanks for that Dave I might give that a try 