I have in the shop right now a Scag Tiger Cub (model # STC48A-20CV, serial # 9261745) powered by a CV20-65597 Kohler. It's blowing one of the two 20 amp fuses, and I haven't figured out why just yet. Hopin' y'all had a better idea than me.
The fuse will last for maybe 2 or 3 minutes while mowing before it blows out. I discovered that this particular fused circuit is used by the charging system and the fuel solenoid. The other fused circuit (starting, PTO, hourmeter) is OK. One strange symptom I discovered is that the charging system doesn't work when the PTO is activated, but as soon as it's deactivated, the battery is charging again. The fuses have been blowing when the PTO is activated. The customer says he recently replaced the PTO switch himself not very long ago (exactly how long, I don't know). The switch he has is the 8-terminal Delta switch (Stens #430-798) which is the correct aftermarket replacement.
The charging system itself is fine. Stator puts out plenty of AC volts, and the regulator passed all tests (I tried a new regulator just for the heck of it -- no difference). My guess is that when the the PTO is activated, the charging current is being shorted to ground somewhere. Wouldn't that account for the battery not charging and the blown fuses? I can triple check, but the DC wire from the regulator looks good and doesn't appear to be touching ground anywhere. The most likely culprit seems to me to be this enigmatic little box called the interlock module (reference #17 in parts diagram). This thing looks like it's a part of every circuit in the machine. I don't really know the operation of this little jewel (over $100), and I don't know how to test it besides trying a new one. But I'd like to be reasonably certain that's the problem before I buy one.
I verified that the fuses are supposed to be 20 amp, and the charging system is rated at 15 amps. 14.8 amps is the highest reading I was able to get out of the charging system. The only other component I haven't comfortably ruled out is the relay. But I've never seen a relay cause a problem like this.
What do you guys think?