[russell_w_b]

Did you connect your existing wire to terminals 2, 3 and 5 of your socket when you managed to get behind the bookcase, so bringing them out to a point in your existing bell where you can work with them?

You need to have all three connections readily available at either your existing bell or your N1071 (which I take you to be connecting without fitting a 'slave' LJU) before you can make progress.