A simple trick to help find a short quickly-remove the wire from the fuse and wire a
12V lamp socket in series-one wire to the fuse and the other to the wire you just took off the fuse. Put a
12 volt incandescent lamp in the socket and insert a new fuse, it will not blow. The test lamp you just installed will glow brightly because it is getting power from the fuse and ground from the short. The lamp limits the current so the fuse will hold. Start taking stuff apart or jiggling stuff, I like to try and guess where the approximate middle of the circuit is and separate it there which tells me which half has the short, then split that half etc till you narrow it down. When the test lamp dims or goes out you have disconnected the short. Sometimes it will go out but if there are other loads like lights switched on the test lamp will still glow but not as bright as the loads will have resistance and are in series with your test lamp. The more loads the brighter the test lamp so try and have all your switches off.
I have done this many times with house AC wiring as well and it enables us to drill down to the location of the short very quickly which always amazes the customer who spent days taking stuff apart and poking into everything before calling us.
The other tip is look for the obvious, any screws been recently installed? BTDT. Also turn off all switches, it may point to the fixture or wire run that is shorted if the short goes away with the switch off. Also, if the switch is off to a fixture and the short still exists you know it's not that fixture causing it so don't waste time pulling it (provided that the positive wire is the switched one). Switches can move around too and short against the metal, fixture screws can be driven right thru a wire.
I can't stress how important is is to turn off all your switches, that simple act could find the short very quickly. BTDT