The terminal posts on these wall connectors are known as KRONE, insulation displacement type. I can see from the photos that you don't have the insertion tool (used to be 70 quid + in the early 80s, Lord alone knows how much now). The reason I say that is that I can see you are using the way we used to do it when we didn't have the tool, i.e. bridge a large piece of the wire across the contact cutters and then force down the wire on each side with each hand. You then trim off the excess. It works pretty well, but not always, and relies on the perpendicularity of the wire across the blades.

There are a few conditions:

- Krone connectors simply do not work well with multi-core wire; they are designed to take single core telephony wires. UTP is not always single core, which you would need to check.

- if you do use multi-core, there is no guarantee that the insulation will be cut properly on insertion, since the wire bundle tends to collapse under the compression of the blades, hence it looks as if it has cut OK, but hasn't.

- you cannot use overgauge insulated wire, or the blades seperate under insertion and do not cut the insulation, as above.

- you cannot use the double insulated wire that looks like it has the right gauge as it only cuts the outside sheath, and not always the inner. Again, as above.

- some UTP cable actually uses a nylon thread core, with copper ribbon woven in for conductivity. This type of cable is used for IDC type connectors, but the sort that cuts into the thread perpendicular to it, along it's axis (RJ type connectors). The thread collapses if you use lateral blade IDC devices, across it's axis.

From your symptoms, you describe one dead IDC joint in 16 connections; not inconceiveable.

You should be able to make a loopback test adaptor by taking an RJ connector with a short length of cable. Loop back 1-2, 3-4, 5-6, 7-8. Plug it in the wall socket and go to the other end. With a multi-meter, ping out 1-2, 2-3 etc. and if all 4 loops are good, then you have made 16 good joints, 8 at each socket. If any one of the pairs fails, then you should re-make all 4 joints for that pair at both ends of the cable.

Not trying to be critical, since I suspect (as you say) that you are good at this. However, this advice comes from 4 years of frustration with this IDC system working in Telecoms, where this problem happened over, and over, and over again wasting many hours trouble shooting. For wall fittings, I would always go for screw or clamp connection types, never Krone (unless I had the Krone cut-and-insert tool).

The Farnell part number for the insertion tool is 147-894.

And no, I no longer know where the one I stole^H^H^H^H^Hborrowed back in 1986 is, sorry!

Are there any small telephony companies that do office exchange installations anywhere near Signet Court? Maybe you could borrow the tool as I am certain they would have one. They wouldn't be able to exist without one!