I am using a 1996 Ford 5000.
have had similar problems that were previously "solved??" by jumpering the starter.
not the way to do it.
on ours there are two start safety interlocks.
the gear lever needs to be in neutral and the high - low range lever needs to be in neutral.
the switch on the high low range selector seems to be crudded up a little and can take a few gear selections to come good.
the interlock switches are there for your protection. work with them.
great airfield tractors BTW.
PS. one of the owners was miffed by the guys selling copies of the maintenance manual so he has it as a free download.