Are the hazard warning lights working? If not, check the fuse, as they are on the same fuse as the reversing lights.
If the fuse is ok the switch is on top of the gearbox towards the front. It's easy to test the switch, just unplug it and use a multimeter to check for continuity when it's put in reverse.
If removing the switch it's easier if you take out the battery and mounting tray first.
Brian.J.
August 2008