Ceiling rose to new light fitting

One of the reds is a switchwire, this needs to go in terminal L the other two reds are permanant lives, these two need to go in the lop terminal or put a connector on them. Really you need a two prong tester to find out which one is the switchwire.If in doubt call an electrician it’s about half an hours work.

Two of the Red cores are permanent live they need to go in a block together and the 3rd red core is your switchline which goes into the L of the fitting . you need to use a tester to test witch one is the switchline back . call an electrician to help as wont take long to sort out . or if you put 1 red into the fitting and the other 2 into block if the light stays on thats a permanent live do this with all 3 reds and the one that does not keep the light on will be the switchline

One of the red wires will be the switch side.

The 3 red cables are your live loops or permanent lives. 2 of the blacks will be neutrals and one the other blacks will be switch line. You really need to know which one is the switch line and if unsure get yourself an electrician. That is typical configuration for a ceiling rose and without proper testing you can never be certain. One of 3 things will happen if not correct. 1. Wont work 2. Permanently on 3. Short circuit Be safe!