I have a 91' Thomas that wouldn't start half way through it's route. Tried starting from front and rear with no luck. Replaced batteries and tried, nothing. Jumped it at the starter and it started right up. Drove it back to the shop and now it starts every time. Bad starter?
start by checking the wiring at the starter and starter relay- tightness and cleanliness. I had one that was just loose enough that if I wiggled the wire when it wouldn't start, it would make enough contact to start.
Check the (+) and (-) junction posts on the frame rail. They should be located right behind the battery box. On our FE's they tend to get a lot of corrosion and break apart. They are a mess to replace.
If you had power with the key on, but no start, check the switch at the engine compartment that is pushed in when you close the "hood." I don't mean the "Run/Stop" toggle, or "Start" push button switch, but there should be a metal plunger switch that closes when the engine compartment door is closed. We've had the brackets that hold them bend just enough that the plunger doesn't go in all the way.