Electroserve said:
Turn you power supply off to the lights and take off the light switch there will be a black and red cable, place the red cable into a connector block with the earth(green/yellow) cable, using a multi meter test at the fitting between all black cables and earth(green/yellow), till you find continuity between this cable is most likely to be your switched live mark it with red or brown tape. and connect it into live on its own
Or check continuity between each set of red and black whist turning the switch on and off.
Much easier than disconnecting anything
Also, you mention connecting the red and earth together but checking continuity between blacks and earth. Typo?