Fuses are cheap. If you can't measure the current I would recommend you use the fuse for the wire size.
Good chance your wire will be 14g, 15 amps.
I rewired my Jubilee using 14 wire.
No rule against using a smaller fuse. Fuses are cheap.
I worked on a lawn mower that was wired with 14g and it came from the factory with a 20 amp fuse. I guess JohnT didn't fork for Husqvarna or they would have used a smaller fuse.
The mower was blowing the 20 amp fuse. Come to find out, the power wire on the electric clutch, PTO clutch, was shorted to ground.
This redneck just cut the plug and made the power wire the ground wire and the ground wire became the power wire.
Then I fused the PTO with a 10a fuse..
All is good.
I rewired my Jubilee using 14 wire. Each circuit has a different fuse. Lightning, ignition, alternator, and gas solenoid.
Using fuses for different circuits makes it very easy to tell what circuit has a short.