Think of an upside down Y. The main feed is the trunk, the bottom of the Y. Each supply line off the Y is going to a "user" which is what the electrical schools called it.
As long as that junction of the Y is before the first user you are ok. Doesn't need to be all the way back at the fuse box, can be just before the first user, just needs to be separate.
Take a testlight/voltmeter and you need to measure voltage at each user, with the other one disconnected.
So you can run a 14 gauge wire from the fuse box/ignition switch/toggle switch, wherever your supply is down to the area of the users. Then a junction of 14 or 16 gauge wire to each user...
Examine the taillight(or headlight, or sidemarker light wiring). Power from supply to each user, but usually branched off just ahead of the first user...