[The Philpott]

The special shunts are certainly something that works- most of the time! The failure mode i am more accustomed to seeing on 20 or 40 lamp sets is the entire string fails to illuminate- yet the white-tipped fuse lamp is found to be intact. I then go through the string, flicking each lamp to find the one where the shunt has failed to 'close'. Often it closes when tapped, sometimes a small spark is seen as the resistive layer breaks down and continuity is restored.

Dave