They used that color coding for a long time. My 68 Dart and 73 Challenger are both set up like that. You should have power at the brown wire while cranking. If it only starts when you release the key, it sounds like there is a problem with the brown wire. Check the connections. Make sure they are clean and tight. Check for power on both sides of the bulkhead connector. It could be a bad connection but could also be a problem with the ignition switch.