My FSM has a supplement for trucks in which the last six digits of the s/n start with 100,001 and 300,001. It does have the diagram for the electronic voltage regulator as used with the isolated field alternator. The diagram show the field wires to be (1) green and (2) blue with white tracer. The blue/white wire connects to the ignition side of the ballast resister, along with a red (I presume) from the ignition switch. The other end of the ballast also has two wires, one of which goes to the coil and the other goes back to the ignition switch and provides full battery voltage to the coil when cranking.
Also, the regulator shows two wires going to it labeled I and F. Per the diagram, I is blue and has battery voltage on it when the ignition switch is on. F is the green wire which connects to one of the field terminals.