I took a look at the wiring diagram in the Haynes manual. If #2 fuse is the same as #2 in the diagram, then the following things are routed through that fuse:
- brake lights (through brake contact);
- horns;

Thogether with the small 25 A fuse this 8 A fuse is switched by the main (ignition) switch. Therefore it only gets juice (and burns through) when the ignition is switched on. By disconnecting the brake lights and horns you can try and run the engine. If the fuse blows, then it's the ignition (what's the ignition's own fuse rated at?), otherwise connect the horns and try again. Repeat process for brake light if fault did not occur.

When fuse blows trace the fault in the circuit that was last reconnected. I would not be surprised to see damaged insulation or something like that.