@67Dart273 gave a great explanation.
I just got done doing this to my 1969 dart swinger; I added a relay to my electronic ignition MSD 6AL w/o efi and no ballast resistor. I connected the dark blue and brown wires from the bulkhead together and triggered a relay. The directions I followed I found in 4x4 forums somewhere. It uses two relays to wire my ignition because I also included a kill switch/cutoff. I also wired for an electronic fuel pump; for priming only but can run if mech fails.
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