any ideas
Won't turn over or won't start? Need some more details. If it has a Kubota and the battery and wiring appears good it could be the contacts in the solenoid on the Nippon Denso starter could be arced and not letting it turn over. Not an uncommon problem. It you take the starter out, take out the 3 little screws on the end of the solenoid with the cover sitting upright. The plunger and spring will pull out and you can examine the large copper contacts. If the contacts aren't too badly grooved, you can try sanding them with sand paper to clean them up. Then blow everything off and put back together. Don't use emery cloth as it could cause unwanted sparking. If the contacts are too worn you can get replacements.
Have you checked the battery? voltage when key applied.. change... Does anything else work?