Just spent about an hour trying to dig up my $#&! Haynes manual. It's just about useless.....unless I need a wiring diagram for something.
FWIW, I did this conversion myself. I used a 3 way momentary switch, so you hold it in the up position to light the glow plugs, then push it into the down position to hit the starter. Works pretty slick.
The wire that engages the starter solenoid on my truck (84) is red with a light blue stripe. I believe it goes from the ignition switch, through the clutch safety switch (or through the neutral safety switch if auto trans), and to the starter solenoid. Wire is the same color where it plugs on to the starter solenoid - easiest way to verify you have the correct wire.
Can't help you with the wire color to the glow plug solenoid; mine is a converted gasser so I did that wiring from scratch.