I am looking at the wiring for the Garmin GTN 750 and one of the diagrams (E-4) shows a fuse/Circuit Breaker on some ground wires. See the bottom three pins in this diagram. Is this just a typo?
This is not a typo. The C/B and voltage call-out helps you verify the ground wire is the correct gauge. This is just a way of reinforcing/reiterating the relationship between the wire gauge, volts, and current rating because getting this wrong would be potentially very bad.
It must be a typo, none of the other ground wiring in this or other diagrams show a CB/Fuse. Sure they will show a gauge to ensure its the same as the power source, but the inclusion of the CB must be wrong.