atassiedevil

Get a multimeter or borrow one.
Get a SV wiring diagram too, there are plenty to be found online.


With Ignition on and battery disconnected and a fresh 30a fuse, check for a short between live and ground from the main fuse, then check it again with ignition off. If you get a short with the ignition on, but not with it off, your short is on the return side from the ignition switch. This will help eliminate about 1/3 to 1/2 the positive circuit on the loom.

Check also with the main fuse out that you're getting positive volts at one of the fuse terminals with the ignition on and battery connected.

If you see no sign of a short, start checking the other items, do you get a short with the headlights, indicator, or horn on? Each of these goes to ground and it's easy to eliminate each in turn by unplugging relevant items.
If you're okay here, go to the main fuse box and remove all fuses, with the ignition on, check for short to ground as you insert each fuse. This will help eliminate each subsystem.

Note also, the starter relay if it's old and corroded can come apart, which might explain your problem...
I had one fall completely apart, giving similar symptoms including the blown fuse.