That white wire with the spade terminal attached to the screenwash switch shouldn't be there and neither should the single wire attached to the back of the board beside the white plugs. Presumably the switch is making/breaking contact between them - have you tried joining them together to see if that bypasses the switch? I can't think where the heated rear window switch comes into it unless the two switches are working in parallel somehow but it should be possible to suss it out by tracing the circuits on the pcb, remembering that it is laid out differently on the underside - it's easy enough to remove the pcb by pulling off the switches and white plugs and removing two screws.
That white wire looks as if it has a red trace which means that it is ignition controlled (position 2 on the switch) and goes to the starter motor relay (if you have one) or direct to the starter on an older type. I think that it is only live when the key is turned to start the car. That assumes that the colour coding has been followed but, of course, any old wire could have been used....... Hope this helps - good luck
