any ideas greatly appreciated, rode my bike 500 yards up the road and all the electrics died and the engine, no power at all, got home and checked the fuses. the 20 amp had blown and when i try replacing them even with the ignition off they are blowing, its been at the local garage for two days and no joy...
I,m no expert and before i send it to an aprilia dealer that charges 55 quid an hour and then maybe a bank loan!! i,m thinking the problem is from the battery to the fuse, bad earth on the battery to the frame... not sure until i get the bike back and have a go with a micrometer.. any insight appreciated..

Tonyl, August 2015

The 20Amp fuse blows because a lot of current is flowing - the fuse saves the wires from catching fire.

A high current flows because of a short between +12V rail (wiring) and the chassis.

Take the battery out - put a fuse in (any fuse will do) and hunt around for the low low resistance - for 12V to blow a 20 Amp fuse the resistance will be less than 0.6 Ohms - I don't know vehicle electrics but would expect the current load to be in the order of 5 Amps total through the 20A fuse - that's a resistance of about 2.4 Ohms.

Set the multimeter up to show the low resistance that's causing the problem and bit by bit inspect the wiring - wriggle it about - and disconnect things. Find the rectifier and voltage regulator - remove them from circuit by disconnecting one terminal.

The problem will not be between the battery and the fuse - it will be after the fuse else the fuse would never blow.

The problem will not be a bad earth - a bad earth can only reduce or stop the flow of current.

You're looking for a dead short - could be the wiring but more probably a component device.

A micrometer is a measuring device for very small dimensions - you'll need a Multimeter - set it to Resistance (Ohms). Put one connection of the meter on the battery + wire and the other on battery minus (battery out of course) and leave them there as you hunt around.

A multimeter can be had for just a few pounds - Amazon - Maplin.

After you fix the fault replace the 20Amp fuse and refit the battery...

Good Luck..., August 2015