I refer to the picture and the snippet of schema (post-1 and post-2): https://pinside.com/pinball/forum/topic/williams-jubilee-gi-lamp-fuse-pops-on-start-up -
Lets assume I want to work on the "power-side" of a Williams pin like the "Jubilee". I toggle-off the main power switch - with one hand or with both hands I grab the 24 VAC fuse - accidentally I touch the fuseholder of the 110 VAC main power line --- what happens ?
110 VAC may flow through my body to earth / 110 VAC may flow through one hand, arm, body, arm, hand --- definitely "NO good".
Look in the picture - encircled red is the 24 VAC general purpose fuse (it is NOT the fuse for the bridge rectifier) - and JUST below is the 110 VAC-10-Amp fuse.
Look at the snippet of schema (110 VAC side, on top of the snippet) --- FIRST is fuse - SECOND is main power toggle-switch. You can toggle-off --- BUT the fuseholder / fuse HAS POWER.
So when I work on a pin: I ONLY plug-in the main power-chord when I NEED power for to do some tests. Greetings Rolf