I have an outside light which is connected to 2 T&E flat gey cables, one coming from the consumer unit, the other from a dedicated switch. The two red wires are connected via a connector block at the fitting, so the live supply is switched and the light is not permanently live. However at one point the cables are out of sight, and when they arrive at the fitting I'm not sure which of the black wires is the switched live. What happens if they are connected to the blue and brown wires on the fitting the wrong way round? Is it dangerous? Will the light simply not work?