Eventually decided to change the ceiling light fixture in the room.
The difference between new and old fixtures is that the latter hangs on ceiling hook and the new one should be fixed with two screws.
I have checked the ceiling wiring, and also have drawn the whole flat schema.
Started to drill the holes for screws. The first hole went well, but the second was the pain. Other side of the ceiling from the hook is totally plaster :(
That wouldn’t be a problem, if I hadn’t to hide the hook and the wires.
So I had to put the new fixture aside and to start thinking about two possible solutions:
- hide the hook and the wires with the wiring box, and drill the holes for fixture a bit farther
- cover the plaster part with some wooden or plastic plate and screw fixture on to the plate.