I have a fairly new house, and outside is a lamp spur, with one single cable, 3 core and a copper. I want to add an outside light, upon inspection the cable has been rolled up into a rose type box and is LIVE. The nearest switch in the hallway has two switches, one switches the hallway light and the other doesn’t do anything, but is wired up to the ring I think.

Can anyone shed light (pardon the pun) on why this would be like this and how can I make the light switched.

Could be just part of the lighting ring, with the original intention that it would have a switch and lamp attached. (External trunking ?). or a socket on the ring main?

Not an electrican, but maybe a PIR type light with daylight sensor? but would still be best with an isolation switch somewhere.

copper will be the earth
brown or red the live
black or blue the neutral
grey or the yellow switched live wire these should match the switch you have in the hallway

use for pir with override
see an electrician before you zapp yourself or cause a fire

copper will be the earth
brown or red the live
black or blue the neutral
grey or the yellow switched live wire these should match the switch you have in the hallway

Unless you wired it yourself, never assume anything from the colours of the wires. You have no idea who put that in and whether they wired it up right!

EDIT: One of the reasons I now do all plumbing / electric myself is after finding a Plumber had wired up my shower isolation switch such that it didn’t isolate anything.