Do you have any sort of 12v electrical item? Like a car charger for your phone with a little light on it? The two contacts on the outside of the plug are the negative (-) side, and the one on the tip is the positive (+) side. you could use that as a test light? (Actually, any 12v light will do. If you can get a soldering iron, a light bulb and a couple pieces of wire, you could make a test light.
Since it cranks, there ought to be power coming from the key, but maybe check it? If I remember correctly, there're 5 prongs on the back of the ignition: AM= the incoming power (always hot, top left connector), IG= running ignition power (hot when key is in "on" position, bottom center connector), R= starting ignition power (hot when key is in "start" position, top center connector), ACC= accessory power (hot when key is in "on" and "acc" positions, top right connector), ST= power to the starter solenoid (hot when key is in "start" position, bottom right connector).
To test the ignition switch while it's disconnected, (2 philips screws hold the dash panel on, and the switch is held on by a ring... it's about 10 minutes to pull out) put power to the AM connector, turn the key, and check for power at each terminal in each position. If the switch is good, use your test light and start at the positive side of the coil and move along the wire towards the key, using a needle to poke through the insulation (It's good to solder the needle to the positive wire of your tester to begin with...).
Oh, and this might help too:
http://www.luvtruck.com/PDF/Series5.pdf (link to wiring diagram)
Is this your only vehicle?