Ceiling rose wiring

[Whitty78]

I’ve taken a pendant light out, 3 black wires, one was connected to the brown wire coming from the light the other was connected to the blue, 3rd wire didn’t appear to be connected to anything but it may have come loose when removing the old light and I didn’t notice. I put tape around the two wires I disconnected and wrote on which was blue/brown, connected up to new ceiling rose, light is working fine but now none of the other downstairs lights work, can someone tell me where the 3rd wire should go

 

[JohnD]

You have three cables, each containing three cores (incl. earth)

Two of them are the circuit cables, supply in (from the previous lamp) and out (to the next lamp). These two should have their cores connected to each other to preserve continuity of the circuit.

The other cable goes to the switch, and this will be the one where the black core was connected to the brown of the lamp. You should sleeve this black core with brown to indicate that it is the switched live.

We can deduce that the spare black core will be from one of the circuit cables, and should be connected to the black core of the other circuit cable. When you have verified this, it is useful to mark the "switch" cable with a permanent marker, as "switch"

Ensure that power is turned off at the consumer unit. A light switch does not make lighting fittings safe.

A metre of brown sleeving will last you a lifetime. This heat-shrink variety will cling on if you heat it with a hot air gun or hairdrier. Other sleeving will fall off. Sticky tape will also fall off. You need the 1.5mm size.
https://www.ebay.co.uk/itm/HEAT-SHR...4d869cf3b10fe2b1f82b|ampid:PL_CLK|clp:2334524

 

[SUNRAY]

Hopefully it goes in with the wire marked 'blue', try that first and let us know the result please.

 

[Whitty78]

All sorted, thanks for your help!

 

[SUNRAY]

Well done.
Thanks for the feedback.