If you are in the UK - first determine the make and model of your car and buy a Haynes Manual for it from Amazon - or Halfords - or even your local library.
The Haynes manuals have complete wiring diagrams in the back - you need to concentrate to be able to follow them if you're unfamiliar with the style of presentation.
It is unlikely to be a fuse issue - my guess is the light switch - but I know nothing.
Good luck...
Peccavi
August 2010