car cranks fine in the key start position. Car will not start until you go to the key on position.

Check for power at the brown wire while cranking. Unplug the yellow wire from the starter relay while testing so the starter doesn't spin.

Is this the same for 1967 barracuda?

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.

It's a really common problem, usually is ignition switch, at least on this board.

R.

Always check ignition switch harness connector located where harness exits steering column. At times some of the male/female terminals within this connector can fail to make solid contact, thereby causing this exact problem among other confounding issues.

pull the yellow wire/female connector off of the starter relay to disable the starter. have a helper hold the ign key to "start". you under the hood & see if the brown wire/downstream end connection on the ballast resistor has fire then check the other end of that brown wire back at the bulkhead for fire & if not hot then either the proper wire in the dangling pull apart ign sw connector under the st column or the plug in connector on the ign switch itself depending on what yr you are working with & this "ign2" "crank" circuit needs to be hot. 2 terminal (single} ballast resistor and 4 terminal ECU (or parts house 5 pinner with a dummy 5th pin) system I am assuming.