"Your engine is supposed to ha
"Your engine is supposed to have a 3 ohm coil with an internal resistor. The 1.5 ohm coil is for 8 cylinder application.
The wiring diagram is for the original SEV Marchal or Valeo brushless alternators, which needed field excitation provided via the purple wire. That purple wire is also supposed to have a resistor (around 75 ohm) or a diode to prevent backfeeding of the ignition coil via the alternator (without that resistor, you probably would not be able to stop the engine by turning off the ignition key).
If the previous owner replaced the original alternator with a Delco Remy (or similar) single wire alternator, then you don't need that purple wire anymore. Many of us (including me) have done that conversion, as the single wire alternators are far more common and much cheaper.
If you are not using that purple wire, it should be taped at the end or disconnected from the power source (it is usually spliced with the one that goes to the + of the coil)."