Here is how the ignition switch works on your Dart. When you turn the key to "start" the car, power is sent on the brown wire directly to the coil and bypasses the ballast. When the engine starts and you release the key, power drops off of the brown wire and the blue "run" wire powers up. If you don't have any spark while cranking,(start position)then you have a problem with the brown "start" wire.

Disconnect the yellow wire at the starter relay so the starter doesn't crank while you test. Then, starting at the ignition switch connector at the base of the steering column, test the brown wire for power when the key is held in the "start" position. You should have power on both sides of the connector. If you have power there, then test both sides of the bulkhead connector. Keep testing the brown wire all the way to the coil.

If you don't have power on the brown wire on the ignition switch side of the connector, you have a problem with the ignition switch. On my car, I had some loose connections in the ignition switch connector that I had to fix. I had power on one side of the connector but not the other.