Help Starter key won't start engine

I have a 69 Dodge Dart GT the interior is all stock and nothing looks changed. The guy I recently bought the car from added a new 318. When I went to fire up the car after all finishing touches that the pervious guy didn't complete. Like Carb fan and belts. The starter switch key would not trigger the starter. I then put the key in run position and started the engine up for the first time jumping the starter relay.

Any idea why the ignition key won't kick the starter over but the relay will? What am I missing?