Extensions must come from somewhere. Guessing the old isdn plate.
At carolines parents the main incoming drop wire from the pole as overhead in that village, this wire splits off on the front wall above the main door and goes to the incoming bt socket with the electyronics in like yours and the old splitter box outside as another go through the wall to the only other one in the bedroom. Don't get this as extensions like Andrew says come from the removable front plate of the master but you only have the 1 cable and this has 2 wires going to A and B I guess, if you take the whole thing off the wall to get to the back.
Strange one. need to find the other end of the extension cables, might only be one if the cable daisy chains to the first extension and then on to the other and another, what ever you have. We have loads and some have their own wire and others 2 as easier and less wire ( so better for me , less cost!) they have the 2 wires as then go on to another extension.
Find the extension cables and do this.
Some say 2 3 and 4
what I done is 2 4 and 5, not done 3 as the ring wire but 4 might not be needed as it turned out in this post so 2 and 5.
Follow instructions and me I wound not do pin 3 as ring wire and can cause noise but the iplate thing you have gets around that so try 2 and 5 I guess and 3 and 4 if you want.
Sure other will argue but noo filter plate here so removed the ring wire and did 4 as what I found where different instruction and what I had did not say 4 was not needed. Sure I have a phone that wont work on 2 wire so maybe do the lot!.
Lets see who moans now, always do but I try and say what works for me and goes in the new build that was not wired up and here when I rewired.
goes for me.