If the column is the same as a square body, there is a wide, flat plug near the base of the steering column with about 7 wires in it, and that is where the actual ignition switch is located. The key up on the column just pulls a rod that actuates the switch on the lower part of the column. The plug has the turn signal wiring also, so only about 2 or 3 wires are for the ignition switch.
If you can figure out the color code of the wires, you can unplug the wires and jump between wires to make the same connection as you do when you turn the key. You need to provide constant-on 12 volts to power the truck, and then momentary 12 volts to turn over the starter. You could also do the momentary-on by jumping across terminals at the starter.
Bruce