Is anyone going to have a go at answering OP?I am prepared for correction or to be told that I am wrong but here's what I'd do...........
you need to do a bit of detective work - follow some cables etc and try to find out what those two cables are going out of the light. Assuming that you have identified the wire to the switch and discounted it - it is likely that these wires are the feed into and out of the light. Can you see where they go? You could post a pic of the light fitting wiring?
I would use a
voltage detector to make sure they both remain live when the switch is operated. Also is there an existing fan? Could one of these go to the fan? If there's no fan AND voltage remains despite what you do with the light switch, It is likely these two are the feed in and out of the light.
You need to cut one of the red and black wires somewhere there's some slack and install a junction box (4 way). Red is live, black is neutral, copper unsheathed is earth. You need some 3 core and earth wire coloured black, brown, grey and unsheathed copper earth and a bit of 2 core and earth with brown (live), blue (neutral) and unsheathed copper earth. Run a length of 2 core and earth from the JB to the pull cord and a length of 3 core and earth from the JB to the 3 pole isolator, and from the isolator to the fan
You need to connect to the two red lives of the existing cable to the brown of the 3 core and the brown of the 2 core. Then connect the two black neutrals of the existing supply to the grey of the 3 core and earth (usual to apply some blue
sleeve or even blue insulating tape to identify the cable as neutral. Connect the Black cable from the 3 core and the blue cable from the 2 core into another terminal and sleve both brown (this is the switched live). In the final terminal sleeve all the exposed copper earths seperately in green and yellow sleeve and screw down tightly.
At the pull cord connect connect the brown to the common and the blue (sleeved brown) to L1.
I have now found a diagram I have modified as getting sick of typing
Note the sleeving of the various conductors - makes it easier for yourself and any spark who may come along later.
Basically:
red is old and brown is new
live
Black is old and blue is new
neutral
If wiring already protected by RCD that should be fine, but push the test button a few times to make sure it's working!
Where is the fan going to be positioned? Is it a 12V or a 230/240V one? There may be a transformer required too.
Don't prat about with 5A junction boxes get a decent sized 20A+ and they are far easier to work in.
I stand back to be corrected...
