Key ON power is supplied to the Black, Brown and Brown w/White wire. Basically everything is powered up. I would disconnect the ignition switch first to make things simple, no that's not the problem. Now use a jumper wire from the Red wire in the harness side of the connector and connect to the 3 output wires each in turn. When the fuse blows you will know which circuit has the short, Black, Brown, Brown w/White. You'll need a supply of fuses, they don't have to be 15A but can't be higher than that. Once we know which circuit is at fault it's a case of tracing down the components and disconnecting them. If that doesn't solve it then there's a ground somewhere in the harness where it's rubbed through the insulation, you can do a harness inspection first looking for and repairing any damage.