Sorry m8, should of worded it better, the timer relay is usually the faulty one but either relay being faulty will stop the light in the switch coming on, the light is fed from the power to the heated window so if there is no power getting there then the light won't come on.
Put your hand on the relays and get someone to operate the switch you should feel both relays click, if nothing then the timer relay or it's wiring is faulty, if only the timer relay clicks then the power relay or it's wiring is faulty.
Also has the windscreen recently been replaced or any work done around the scuttle panel area? This is where the connectors for the front screen are.
Also check fuse 22 this supplies the power to the switch and the timer relay.

Steve