Car cranks but wants to start when i release the key but wont run

Jake1974dart said
maybe you guys can help me with this headache. Right now i have a small block 408 1974 dart and i am having trouble with start up. I have an electronic ignition with the orange box and the msd blaster ss coil with a recurved stock distributor. I have already replaced the box, original coil, ballast resistor, and ignition switch in the column. I dont know what else could be causing this situation. Any suggestions will be a big help.
-Jake

Fought the same battle with the exact same symptoms. I changed everything just like you have. I deduced the only thing left, after checking and making sure that I had 100% good grounds, was the electronic ignition wiring harness. Ordered one and installed it, problem solved. Don't know if that is your issue, but this sounds very familiar. Haha
After inspecting the old ECU connector, it looked to me like the socket for pin number 2, the wire that actually sends the signal to the negative side of the coil, was pretty sloppy and wallered out. As was pin 4 and 5 the wires to distributor.
And I can't logically tell you why that would have anything to do with the no start scenario in crank but start in run. I'm just saying don't forget the wiring, cuz it's 40 to 50 years old unless you already have a new wiring harness. In that case, never mind. LOL