Get the test light and your factory service manual out. Find the wiring diagram for the ignition switch out to under the hood. Look in the book and see which wire is hot for the ignition when the key is switched ON. Switch the key on and start probing that wire under the dash on out under the hood and see where you stop getting power. "I" would assume that since it runs in the start position that the fusible link from the starter is GOOD, otherwise there would be no hot signal from the starter. Follow the diagram and probe with the test light. You will find the problem.
