Re: Warning Lights
In the BBC, up to at least the 1980s, we used butterfly fuses...
Ah the nostalgia... those fuses were used on anything operating from the - 50 Volt Station Battery...
Too many years ago I worked in the (then) BH Ext in London, more or less overlooking Duchess Street. What I was doing at the time is long forgotten but on one occasion I was working on something on a temporary feed from one of those fuse panels, and in simple terms things weren't performing as they should.
Switch off; check supply voltage; nothing wrong there. Switch on again; problem still present. Check voltage with equipment connected... aha! That's a bit low.
Some comedian (longer in the tooth than I was) has replaced the fusible link with a resistor, rendering the "fuse" somewhat useless.
For the uninitiated the fuse wire (or resistor, as the case may be) was actually invisible as the butterfly's wings concealed it when the wire (or resistor) was soldered in.
Oh happy, innocent days... mostly anyway.