That's exactly it. The room switch just to operate the room light and the cupboard switch just to operate the cupboard light. Totally apologise for the lack of info.
Seems to be huge misunderstandings with this. I have one room with a cupboard in the room. There is a room light controlled by a switch. Inthe cupboard there is a light and also a switch.
At the light in my cupboard there are two red cables and two black cables. At the switch in the cupboard there is a red cable and a sleeved black cable.
At the room light there is a red cable and a black cable. At the switch there are two red cables.
Okay got the picture now - but I fear that your problem may not be solvable without rewiring part(s) of your lighting circuit..
I will assume that the main room switch (two red sleeved conductors - going into C and L1) that operates the main room light (one red sleeved conductor and one black sleeved conductor) is working correctly.
Your cupboard light (2 red and 2 black conductors) and your cupboard switch (1 black cable (red sleeve) and one red cable. Red to C and black to L1).
You had a problem with the main light when when you wired the cupboard switch up.
Under normal circumstances I would expect the main room light to have at least 2 red and 2 black conductors plus earth. Yours does not so the main room switch wire is possibly getting its power from either another ceiling rose (possibly the cupboard light) or more likely a junction box hidden somewhere.
I would advise that you look up lighting on the wiki and learn and understand how lighting systems work.
After that I am afraid your only real choice is to utilise the services of a multi-meter and try and track down where each conductor goes. If you do not have one or do not understand how to use it then it may be prudent to call out an electrician.
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