There is only one RELIABLE way to check fuses, and that is to check the voltage on both sides UNDER LOAD
That is, example, if the tail lights don't work, turn on the park/ tail lights, and check with either a lamp or meter on BOTH sides of the fuse, CONTACTING the fuse clips (holder) NOT the fuse.
Only then do you know that power is actually getting through the fuse
Believe me, I've screwed with electronics/ electrics most of my life, and I've been fooled a few times along the way.
Also, ESPECIALLY with these old girls, getting older everyday, suspect poor connections right in the fuse panel