Simmtec made a slip when he said Brown/Green.I have is two white wires connected to one terminal of the switch and a brown/blue connected to the other (with no other wires). This differs from the brown/green mentioned above and I could not see anything matching that description.
If you reference the diagram that simmtec posted, they are numbered 9 and 36, which are White and Brown/Blue..
I'm afraid Mike really confused me, and perhaps you, by referring to an Electric Screwdriver. Only when I looked at his link did I realise he meant a Circuit tester.
The back of that looks normal, so however you go about it, circuit tester, multimeter or test lamp, what you need to do is check (when the Battery Isolator is ON) if the battery voltage is on the terminal which those 2 white wires are connected to.
That will confirm that the switch internals have shorted out.
If that is the case, then you've nothing to loose by taking it out of the car and taking it apart to see if it's fixable. It's no use to you at present.