as suggested do a search for a typical wiring harness
wire depends on the application/load of a particular appliance, ie, alt. ampmeter(if used, but many do not recommend one) use a volt meter instead, led's, head lights. read about relays and how to wire them. main wire to fuse and relay panel should be large enough to handle all loads. lots to know and FUN to learn about.
there is lots of information about this as well as some home made wiring diagrahms to bee seen
i made my own harness and remember to keep good notes and diagrahms
drum52 has an EXCELLENT one
good luck ... have fun
here is but one of ...
https://www.stovebolt.com/ubbthreads/ubbthreads.php/ubb/showflat/Main/15166/Number/102087#Post102087
