I would take a test light to the starter solenoid to see if you have juice. If not, from there check the clutch safety switch (if it has one), then the key switch in that order.
Did you try jumping right at the starter to see if it would crank the engine. Large terminal where battery connects to small terminal on the solenoid. Just across there to see if it will spin over. (make sure it is not in gear) if it's a manual setup.
When I jumped across the dozer starter it started and ran normally. Took the “dash” apart as far as possible; however there is not any slack in the lines. All leads (four) on the switch seem in good shape and are firmly attached. The problem may lie with the switch itself. Does anyone know where a replacement switch can be found in the US? OR is there an “universal” that would fit and do the job… available from one of the local auto parts store. Does anyone have a wiring color indicated diagram for the switch? thanks,
The Ford cold-start tractor switch will do the job for you, I think. Might have to use a multimeter to suss out the exact wiring, but shouldn't be too difficult. Here's one source: