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?

[SGT.SNAKE]

No resistor is simply for the electronic distributor and ignition coil. This keeps the car alive and running outside of a tachometer failure.

Original wiring config., with resistor, tach fails? Car does not start.

[Rcbach302]

I believe you are looking at the ignition switch pigtails. The factory tach harness has two separate leads that plug directly into the the bullet connector leads coming off the tach. The tach is part of a series circuit that does connect to the pink resistor wire in the harness. And yes if the tach fails, you have no spark, hence why some people have them re-wired to be on a separate circuit. If you are replacing the ignition switch pigtail, the one with the pink wire is correct.