1972? Seems like there is a bakelite junction on the front of the truck by the battery where a wire from the positive side of battery is joined with another wire on a single stud.

This is located between the battery and the radiator.

If this wire is bad or the connection to it is bad, nothing will happen when the key is turned on.

The reason you have power with the starter turning the engine is because of the by pass wire to the ballast resistor that comes off the battery solenoid.