I have never seen the subject generator, but if it is a "mechanical" diesel, all it needs is fuel, air and adequate cranking speed to run. Check the fuel solenoid if it has one, usually they require voltage to run, remove voltage to stop. See what it does in both auto and manual cranking attempts.
Since you mention a mag pickup, I'll guess you have electronic governing with a rack/throttle positioner, the same goes for it. See what happens in auto and manual cranking.
Yes, electronic governor. It is a Generac with the 3.0L John Deer. The voltage from the mag pick up is between 26-29v, the voltage from the mag pick up for the RPM sensor is 1.5v. Will recheck every thing after I go back to work next week. Just looking for ideas.