I know its an elementary Question, but have you checked that you're using the correct size fuse ?
You could try going up one size.
Alternatively, decide if it blows when you use the horn or when you use the starter.
If the horn, trace the wire leading to it and you will find a rub somewhere.
If the starter, disconnect the small wire to the solenoid on top of the starter, press the starter switch and if the fuse blows you know you have a short somewhere on the wire from the switch to the solenoid, it will probably be an extremely small rub some where on the wire.
If it doesn't,..... then make sure that the tractor is out of gear...., and run a thin wire from the large live terminal on the solenoid and touch it to the small one, if there is a large flash then your solenoid wants replacing, there should be a small spark and the starter will turn the engine.
Hope this helps, Dave
