Hi, I've recently attempted to replace an old ceiling light fixture (3 spot light). From what I've deduced after some tinkering is that there are wires from the 70s that are two grey cables containing live (red), neutral (black) and ground (bare) and a white cable containing the same. I'm almost positive that the two grey cables correspond to the ceiling light and the downstairs bathroom, and the white to the switch. I'm at the point where I've left the white cable's live, ground and neutral unconnected but the downstairs bathroom switches on and off it's just the ceiling light in the kitchen (the one I'm wiring) stays on.

What wire goes where?

I am having a little difficulty following your post.
I understand that you are replacing a ceiling fixture. In the ceiling box you have two cables. One is a three conductor cable with a red, black and white wire. Three conductor cable has 4 wires. The fourth wire is the bare ground. The ground is not a conductor so we don't count it. Note that it is 3 conductor not 3 wire. The other cable is 2 conductor with a ground.

With that all aside, I'm not sure what is happening with the downstairs bath. I think you are saying that something is not working.

Only one wiring method I can think of at the moment that would have one 3 conductor and one 2 conductor in ceiling fixture.

To confirm please remove switch cover plate and tell me what wires you have there. Probably find two whites connected together, two blacks connected together and connected to switch. Should have red connected to switch.

I'm confused. I received an email to say someone replied but no reply is here... Very odd.

Hi! Sorry your post wouldn't show up originally.

There are three cables: two grey and one white in the ceiling. Each contains only three wires (red, black, bare copper). For some reason the downstairs bathroom is connected to these wires.

The switch has a green at the back and is connect with black and red. Just to clarify I'm from the UK so I think it might be easier to refer to things as 'neutral, ground, live' if the colours complicate things.

Thanks.

I think it might be easier to refer to things as 'neutral, ground, live'

Agree.

Your wiring system and practices are a different than ours so I am a little hesident. Here is what I suspect. You have one cable bring power to the ceiling box. You have another cable taking power to the bathroom and a third which is what we call a switch loop.

You need to identify which is power coming to the box with a meter, if you don't already know. You then may be able to identify which cable goes to the switch by the color of the sheathing (grey or white). The third cable would go to the bath.

You would then connect live of the power in cable to the live of the bath cable and to one of the wires going to the switch. ( In US it is the practice to use the neutral colored wire to go to the switch and the live colored wire to return.)

Connect the neutral of the power coming in, the neutral going to the bath, and the neutral of the light fixture.

Connect the live of the cable to the switch to the live of the fixture.

If you cannot determine which cable goes to the switch by color, you can connect the live and neutral of power in cable to the live and neutral of either one of the other cables and then check the fixtures in the bath. Just make sure that the switch is in the off position. For safety and to prevent tripping breaker it might be best to disconnect wires from switch and cap with wire nut if you have to do this.

Of course all grounds get connected together.

You're an absolute gem! All are connected and now going off and on as they should. I'd already worked out the white cable contained the conductors for the switch, it was just a process of elimination to work out which grey cable was for the bathroom.

I could kiss you! I definitely would never make an electrician lol. A seemingly easy job has been winding me up for days.

Thanks for solving this little mystery.

Kelly.

Great, congratulations.