Ping kráftéé ? Advice needed to trace wiring fault.

My apologies if this post appears twice. Having posted it, PlusNet's
usenet server had problems and my original is not now shown on the
server. I have no way of knowing if it has been correctly posted at the
moment, hence this repeat.

Tomorrow, I am going to try to help out a neighbour and attempt to trace
a wiring fault. I could do with any suitable advice before starting.

The situation is this:-

He has just been enabled for broadband but could not connect and asked
me for help (not that I know very much).

He has two telephone extensions leading from the master socket and his
computer is using one of them. He is using a router but the DSL light
was not showing.

When the router is attached to the test socket of the master socket, the
DSL light comes on. When the router is plugged into the front plate
socket of the master socket, the DSL light stays off. I therefore
presume that there is a fault in his extension wiring.

What I propose to do tomorrow (please correct any mistaken assumptions) is:-

Expose the connections at all of the sockets, run a length of spare wire
(bell wire) between them and test each telephone wire for continuity
(using the bell wire for the return path). This, I hope, will show where
the fault is and enable us to correct it or re-wire as necessary.

Any comments/suggestions are welcome, please.