Isolate the circuit by throwing the breaker / pulling the fuse
All you need to discover is which cable connects to the shower and which cable supplies the power - the neon light in the switch will tell you all you need to know.
Tape over the tails on one cable to make it safe and connect the other cable to the switch Supply side.
Reapply power and operate the switch. If the neon light comes on and off as you operate the pull cord then it's correct.
If the neon is on all the time then you have accidently put the supply cable into the load connectors.
If the neon fails to light at all you have fitted the load (cable to the shower) to the supply side. The other taped up cable is the power supply
Take care...Good luck...
Peccavi, February 2009