1968 Shelby with Factory Tach Ignition Wire Pigtail

[ramrace]

Speaking of wiring, if I am correct, looking online there are two types of ignition pigtails for 1968 Mustangs/Shelby's equipped with factory tach. One pigtail has a resistor wire the other pigtail does not. The w/o resistor pigtail has 6 wires, the w/resistor pigtail has 7 wires.
 
1. Can someone explain why there are two options? 
2. Can you use either option on the same car?