+1 on what Baz advises. I recall 'Dan Hatfield' posting on the US GT Yahoo group extensively on problems just like yours. He points out that nothing thats working properly on a Kettle is capable of drawing enough current to blow the fuse. So it must be something odd in the wiring and if for example you just played with the alternator (one of two top candidates for high current draw when defective) my bet is its that. Simply disconnect the plug under the left side panel and see if the problem goes away. If so, and if you have moved the wiring to it, that will surely be the place for a fix.
The only other viable alternative will be a wire whose insulation has rubbed away so that you have a straight short. These can be a PITA to find, but made easier by finding hot wires and worse, melted insulation - so take the tank and panels off, open the headlamp and feel for what gets hot when this is happening.
The momentary turning of the fan isn't a problem - mine used to do that and its a small current draw anyway.