Bt Master socket

Only two wires from drop cable to master socket, usually orange & white & go to connections A & B
If older drop cable then you will find Orange, White, Green and Black wires,but the active piar are still Orange, White.

 

A mess, 2 Blue & White & 5 White & Blue are use for the internal extensions.

There no need to connect the ring wire (3) nowadays.

 

This is an excellent read and puts it clearly into perspective.

https://www.btengineerlondon.co.uk/can-i-move-my-master-bt-socket/