Colyn,
The LED indication is not integral to the fuse holder, but added externally. I go the idea from an article in Sport Aviation about 15 years ago. If you put the LED in parallel (w/resistor) to the fuse, it will light up if the fuse is missing. This does assume that there is continuity left in the electronic device down stream. If it were to have a total melt down and become an open circuit, the LED would not light.
I used a similar principle in a push-to-test circuit for the landing light. I check for continuity in the landing light by passing a few millivolts through the filament and lighting up a LED.
Chris Zavatson
N91CZ
360std