wadatah5,
As 'wrenchbender' hinted at above, if your rig is a 12 volt system, and you have a ballast resistor in the primary lead wire, this is a "classic" failure.
The ignition system is powered in the START position, but because there is an open in the resistor, it is dead once the key returns to RUN.
This is a obvious scenario, but it isn't the same as the truck actually starting, running and fizzling out...that is a different animal.
Stuart
