In my first house that I bought I couldn't find the fuse for the downstairs lights. Old rewireable board with 2 white fuses carriers, (5A lights), 1 blue, (15A didn't appear to supply anything) and 2 red, (30A 1 x ring circuit for whole house and 1 x cooker socket).
Finally found out the lights were somehow connected to the ring main but, search as I may, couldn't find where. Then some time later I was ripping down the lower ceilings when I discovered a 13A single socket screwed to the side of a floor joist few by 2.5sqmm T+E cable. Wondering what the plug was feeding I pulled it out and the downstairs lights went off! Plugged it back in and they came on again. Problem solved and re-wire needed. LOL
Finally found out the lights were somehow connected to the ring main but, search as I may, couldn't find where. Then some time later I was ripping down the lower ceilings when I discovered a 13A single socket screwed to the side of a floor joist few by 2.5sqmm T+E cable. Wondering what the plug was feeding I pulled it out and the downstairs lights went off! Plugged it back in and they came on again. Problem solved and re-wire needed. LOL