1972 dart - stopped running while at 50 mph ? no warning

"zero ohms" resistance with a meter. Usually you can tell by examining the end terminal. The wire should be exposed, folded back, crimped into the terminal. "Blackish" looking "wire" is almost always resistance. You don't need to use a spark plug/ high tension wire. You can just use low voltage wire, "or even bare" but just keep it away from metal etc

It is likely that the "mag suppression" will be a wire type. They are usually some sort of spiral or other technology to help RFI