Did you ever fix your mower? This is the same identical problem I am having with my Scotts mower with a 17.5 Kohler engine.
I have checked thoroughly for a shorted wire. I pulled the flywheel off and checked the armature for damage and it is fine. Measures about .3ohms so no excessive resistance. Not sure if this is a good spec or not. I have had one of these before that the magnets came off of the flywheel and ate up the armature.
Regulator has high resistance, in k ohms range between all poles and ground.
Does not blow fuse with regulator unplugged but does not charge battery. (Duh)
With regulator plugged in it charges 13.5v and blows the fuse in approx 10 seconds. The fuse in 15a, does not blow a 20a fuse but it does get hot, and it does charge that battery.
Thoughts? Does anyone have regulator or armature specs?
Thanks for the help