Check the Wire Sizes
Disconnect the main switch, and determine the size of the wires in each circuit. Don't include the insulation in your measurement.
BE CAREFUL!
Even though you have disconnected the main switch, the wires coming into it are still "live". So, do not touch any wires. Instead hold the wire size chart near them so that you can tell which gauge each one is.
Write in the proper size fuse for each circuit on your chart.