I have a property that is just over two years old and i tried to install a ceiling light in the rose for the first time. Unfortunately it failed to work. I tested the switch with a simple circuit tester and that seems to work, three red wires coming in on the common and 1 black on L1. The ceiling rose has one black and red. I know the red is live because i put a mains tester on it but i do not know the condition of the black. The light fitting works fine when connected elsewhere. Any help in solving this would be appreciated