mm will help you when he gets back from the pub...
He doesn't like me to offer electrical advice because I'm not a qualified electrician - he thinks I'm dangerous and sometimes I use words that confuse him...
Nevertheless...
A light switch has only live wires in it - permanent live going in and switched live coming out - to turn the light on.
There is no neutral wire - anything you connect to the light switch will not work because there will be no neutral return path to complete the circuit.
The solution to your conundrum will be found at the light fitting on the bathroom ceiling as mm has suggested.
You will do best to examine it (the fitting) and report back to him as he asked...
Good luck...
Peccavi
August 2013