Use a test light in place of the fuse. Get 2 male spade terminals and make up wire ends. Then leave the test light (or other 12v bulb) in that fuses place. Then turn the lights on. Start unplugging everything. If the light goes out then you know where the short was. It will be on as long as any bulbs are in and running so those will need to be unplugged. Eventually if nothing then its in the harness
Check the circuit diagram too and make a not of all the components that fuse supply's power to
Check the circuit diagram too and make a not of all the components that fuse supply's power to