Inline fuse engine compartment question.

[8door]

Going through wiring ,wire by wire, comparing to wire diagram.So far found two problems.
My truck has two small fuse holders, one has no fuse , but the other
the clip holder is broken. The buss fuse has a 4 amp rating.
Looking at the wire diagram there are fuses and on either side near fenders.
There they are sticking out of the wire bundles and look like small rubber eggs about 1'' long, both connected to the main power junction on the passenger side fender next to battery.
The diagram calls them Eg. Harn. Conn. I assume means Engine Harness Connection.
What are they protecting ?
Is 4 amps correct ?
Why two terminating at same spot on firewall connector ?