In message , Graham J
writes

What you've written does not make sense. If you take the fuse out of
course one side of the fuse socket will have voltage - from the
battery; and the other side - to the light - will not.

So if the fuse is good it will carry the current from one side of its
socket to the other. What might be happening is that the fuse is not
connecting properly in the socket. Or that when mechanically stressed
by insertion into the socket it actually goes open-circuit. I suggest
you try a new fuse in its place.

Or swap with the good one?


--
Tim Lamb