Thinking about it, there are essentially two strategies to dimensioning the fuse by the battery;

* Fuse to protect the wire - ie just to make sure it doesn't turn into a glowing red hot wire that sets the interior on fire... Fuse size is determined by wire gauge (and possibly whether it's run in open air or "embedded" behind panelling, in wire bundle or under carpet). Requires additional fusing by/in the products supplied by the wire. No problem hooking up more gear to the wire, as long as you're still below max ampere capacity of the wire.

* Fuse to protect the gear powered by the wire directly. In this case I would actually consider putting a 3 amp fuse by the battery and increase the fuse size in the fuse holder on the wire harness... Much easier to change a fuse by the battery than having to rip out the cage to get to it... Can only supply one product, additional gear requires new wire run.

/Michael