Tractor Repair: Fuse blowing, amp fuse, positive cable

Question
I have a Kmart/Murray 42" lawn tractor with a 14.5hp Briggs and Stratten engine.  When recently using the tractor it stalled out.  When trying to restart the engine would not turn over when turning the key.  I checked the 15 amp fuse and found it blown.  I replaced it with a 10A fuse and it also immediately popped.  I checked the positive cable for shorts to ground and found none.  The 15A fuse is called for by mfgr spec.  The starter always worked,  I checked with the positive cable disconnected.  I find that it will have continunity to ground (machine frame) through the positive terminal so I am thinking that the winding is ok as the starter on my Sears lawn tractor which is working also does this.  I am not sure where to look next.

Answer
Hi John
You seem to have done all the right things , so do you have any other auxiliary fittings on the tractor that could be faulty
and causing the wiring to short out. and blow the fuse !
I imagine you do not have any faulty lights /head and brake light etc I can only suggest that you check all the wire connections and that there are not any bare wires rubbing against metal contacts etc.
Martin