Small Engines (Lawn Mowers, etc.): KOhler 12.5 OHC, starter solenoid, battery cables

Question
I have a Kohler OHC 12.5 on a john deere riding mower at least 15 years old.
The battery is good and the positive has juice all the way to the starter which is
brand new. The ignition is also good however it will not start. When I hook a
boost up to the starter it will start then. My guess is some fuse or switch. What
do you think?

Answer
Have you have the battery load tested?  Did you dis-connect the battery connections and clean the battery posts and cable ends with a wirebrush?  

You you turn the key to the spark position, do you have 12 vDC at the starter post?  Did you check the voltage with a multimeter?

Did you check the voltage at the starter solenoid?  I've had corrosion and old wires or battery cables that could not carry the current to power the starter.

Clean the connections and have the battery load tested.  Let me know what happens.
Eric