Dart dies after running awhile

Check the coil wires, I had a same problem with my 73 Road Runner 10-15 years ago and it turned out that I had switched the (2) wires, that go to the coil, around, I had the positive wire going to the negative and vice versa. It would run for a bit then die, would have to wait a bit and it would start back up, the longer I waited to start it back up (to a certain extent) the longer it would run before killing. Hard on the coil too, can potentialy wipe out the electronic ignition box also.