Switch - normally situated at the brake pedal. Often will just need adjustment (screw in/ screw out) to get it to work again. The brake pedal pushes on a plunger to switch the lights on, so the plunger needs bringing closer to the moving part of the brake pedal that connects with it.
If that doesn't work, then check the connector to the switch - it may have come loose.
If still no joy, check the relevant fuse.
If still no joy check the switch with a multimeter, and if no circuit is being made when it should be, replace the faulty switch with a new one.
ChicksFan
January 2010