Tel sorry fella but i've had to delete that reply because while I know it was said in jest it is in the open forum and it was asked by a Trainee( don't know if you noticed that ) But I know you will understand why It had to go.
no problem, mate. ( i'll get you later. :20: ).
supply and load reversed on switch
Possibly a small induced voltage in the cable....or capacitors in the PCB holding a charge after power shutdown?
It is quite possible that you have water leaking inside the shower and providing enough of a path across the switch contacts to allow the light to illuminate slightly. Well worth isolating the shower and removing the front cover to see if it is wet inside. (and if so finding the source of the leak and fixing it)