[elysianforest]

...Even if it can't, it is totally capable of melting your entire wiring harness if a short occurs.

Arizoni's hit the nail on the head here. This is also why we don't put in higher amperage fuses - 7 or 8 feet of 18 gauge wire can burn if it's got 20 amps on it.

[jefrs]

Examination of the CSA of the wiring in the harness indicates is is good 20A continuous and more intermittent, i.e. good for 240 watts. About 2.5mm², less than 2mm diameter can carry 20A, voltage is irrelevant and the voltage drop over the length of a bike is insignificant.  If fact capable of running a pair of 55W spot lamps (an extra 10A) straight off the main beam wire. Everything-on is about 100W, about 9A - that can be doubled without additional wiring, fuses or relays. RE wiring may be crude but it is heavy-duty.
No, the wire is not going to melt the insulation, the wires are too thick.
The fuses are often whatever RE felt like fitting at the time. The main fuse can be 15A or 20A. The signalling and the lighting fuse can be 10A or 15A (if you switch to twin horns, stick a 15A in). The ECU fuse should be 10A. Total Watts/Volts=Amps for fuse rating, round up to nearest 5A.
The alternator appears to be capable of 220 watts.
Using the ten-times rule of thumb the 14Ah battery can output 140A (for 6 minutes). It can probably output more but at some risk of warping the plates.