After 18 years of jumping my tractor off I finally decided to address the problem. I would like to thank JD110 and Mark777 for advice and encouragement. I am not a mechanic, but what I did was to check all components (starter,switch,alternator,battery) and make sure they were in working order. Then I started following wiring beginning with hot leads. What I found was a corroded terminal inside the wiring hornes. I also found I had a circuit breaker that had corroded post that needed cleaning. My tractor now starts every time I turn the key!!
Big Tom
Big Tom