A good way to go about this is to temporarily eliminate circuits 1 at a time until you detect which circuit. A good half way point is to unsnap the connector from the body to the engine and you will hopefully get an indication which side of things have the problem to start with. That vintage had the wire harness that went behind the starter motor that would chafe and short. Headlight harnesses as well are problematic.

Scotts is Murray. I would first check the starter.

If you did not turn the starter and it blows immediately, Then do this.

Replace the fuse with a bulb . If you turn on and not start and you see the bright light then start removing the circuits one at a time . When the bright bulb goes out that will put you in the shorted area.