Remove the distributor and coil from the truck. Lay it on the bench and wire it up to the a battery.
Put a spark plug on one plug wire and ground the plug.
Rotate the dist. gear by hand. The plug should fire once per revolution. If it does check the rest of the plug wires.
If it doesn't, plug the wire into the top of the coil.
Rotate the gear and the plug should fire 6 times per revolution. If it does, the only things involved in the problem are the cap and rotor.
The contact on the center of the cap has to touch the top of the rotor. The rotor has to reach the plug wire contacts. Rotor can't be shorted and has to lock into the notch on the shaft. The cap can't have a conductive path from the center terminal to ground.
It is that simple.
