When Murdoch replaces the fuse in the electric panel, the hairpin that caused the blackout was still in the lamp. This means that, when Murdoch turned the power back on, it would have blown the new fuse. In order to avoid this, the hairpin had to be removed from the lamp before replacing the fuse.
The knife described as Doc Holliday's around 33:33 is an Opinel, which didn't exist in any form until 3 years after Doc Holliday died, and that particular model with the Virobloc locking collar didn't exist until 1955.