Cabriolet - 1995 - 'M' reg.

I have an electrical problem that doesn't make sense - at least to me
it doesn't !!
The rear foglight won't go out. As soon as the lighting switch goes
into position 1 (side & tail lights) - the rear fog comes on (and the
LED in the switch illuminates too. So - I removed the switch - it is
STILL on. So - I removed the *front* foglamp switch as well - it is
STILL on.
But - with both switches back on the panel, once I turn the engine on,
then not only is the rear foglamp on, but the rear fog switch operates
the front foglights !!
Obviously, there's a fault somewhere, but I can't work out where it
could be. As far as I can ascertain (I don't have a Cabriolet wiring
diagram, only an A4 diagram which *should* be the same) , the +12v wire
from the output of the rear-foglight switch goes direct to the lamp -
no relays or any other connections - so ...... if the light still comes
on when the switch is removed, I assume that the wire must be picking
up +12v from another wire (rear or licence plate feed maybe) somewhere
along the way ?
May be the loom in the boot (trunk) lid, but before I start to
dismantle the rear end of the car, can anyone confirm that there are NO
relays or any other branch connections in the Grey/White wire between
the rear fog switch (pin 6) and the actual bulb in the boot (trunk) lid
??

Many thanks.
D.V.