Long shot question, but I'll try anyway
1996 Ford (new holland) 4600 tractor I use for maintaining the strip wont start unless I turn on ignition then go round to the engine and run a jumper wire from the battery to the starter, when trying to start normally the ignition comes on but the engine would crank similar to the response When the the gearstick or the Forward/reverse lever or high low lever are not in neutral. So i'm assuming it's a "nuetral" sensor on the transmission that's knackered, anyone know where or what to look for before I go pulling stuff apart ?