The ceiling rose has usual configuration i.e two connectors for lamp(+ve) and switch, three connectors for live and three for negative and lamp(-ve). There is a separate connector for earth.
The light switch is fed by two red wires and earths and connects to ceiling rose via one red wire plus earth.
It used to work then failed. I checked the bulbs and thought I had solved it as one of the switch (red) wires had come loose. Reconnecting did not help.
There is 250 volts* ac at the ceiling rose. I have not come across any similar wiring. All other lamps are wired differently.
*UK
Best Answer
Problem solved. The light switch in question was linked to the "live " in an adjacent room switch(i.e two reds on one switch). This had become detached and when reconnected both light switches worked. An odd way of making a ceiling light connection.