In the ceiling rose where the light hangs from you should see three cables terminated hopefully in a terminal block. one cable with black and red cores is the live ring main in from the fuse box. One cable is the live ring main out. (These are always live even when the light is turned off). The other cable goes to the switch. To make the light work current is taken from the ring main cable down the switch cable red core to the switch. when the light is turned on current flows up the black core of the switch cable back to the light this cable is then connected to the live wire on the light. current then flows through the bulb and back to the neural core on the ring main cables. What has probably happened is that the ring main cable has been connected directly to the light fitting so you have the switch bypassed. I presume the light only goes off when the fuse is pulled.
I would get an electrician to test the wiring in the rose to identify which cores are which, it will be simple for it to be put right. Please be very carefull as lighting wiring is often live even when the switch is off. Also black cores assumed to be neutral can actually be live under some circumstances.
Andy, January 2007
