The white wire with black stripe (Circuit #4) is used for the factory electric choke connects to the alternator stator terminal. The power coming from the stator circuit is a very unusual kind of power. It is both Alternating Current (AC), and 1/2 the voltage found at the alternator output that connects to the battery positive terminal. No other current in those cars back then have AC current anywhere outside the inside of the alternator. The 1/2 battery voltage is adequate for the owm choke heating, as the electric choke heater provides supplemental heat, whare the choke housing has a little bit of vacuum flow that pulles filter air from near the carburetor air horn, down to a stove heater at the passenger side exhaust manifold, and the war, heated air is then pulled into the choke area behind the choke cap, where it then warms up the bimetallic coil spring that makes the choke blade open or close. The electric choke heater is supplemental to help ensure the choke opens fairly quickly.
For aftermarket carburetors, were you to ever get one, with electric choke heating, they require full battery voltage to work properly, as they do not have a hot air flow through an exhaust manifold stove heating system. I have seen all kinds of aftermarket electric choke wiring to include using the stator Circuit #4 White with Black stripe wire, which causes the choke to open too slowly. I have seen other folks use the "I" Circuit #16 (Red Light Blue stripe) from the Starter Relay, but again, that has reduced voltage from the resistor wire fed by the ignition switch, as it is routed to the positive terminal of the primary circuit on the ignition coil. When the engine is cranked over it gets "dull battery voltage," which is NOT to say the coil and electric choke get 12 volts while the engine is cranking. Why is that? It is because when the engine is cranking over the battery coltage drops to typically between 9.6 and 10.5 volts due to the huge amperage demand from the starter. When the engine is running the "I" circuit is anywhere from about 6 - 8 volts, inadequate to open the chock as quickly as it needs to be opened.
So, two simple ways to get 12 volts of switched Direct Current (DC) power is to tap into Circuit #640, which powers the carburetor Throttle Position Solenoid (the wiring is present whether a TPS is in use or not), Or tap into Circuit #63 which is the red power wire that feeds the windshield wiper motor. Either approach does pull additional amperage from the feeding circuits, but not enough to cause any problem with overloading either circuit.
If you are concerned with splicing into Circuit #640 or #63 there is another way to accomplish getting 12 volts of switched power to the electric choke on an aftermarket carburetor. You can then run a dedicateed circuit from the relay's "load" side to power the electric choke. I suggest using an inline fuse for the wire between the battery's positive terminal and the relqy's high amperage current source terminal. You can use any number of circuits with a very low amperage load to trigger or activate the relay. The circuits that come to mind for me would be Circuit #4 (AC power at 6 volts is enough to trigger many relays), the Starter Relay "I" Circuit #16 (Red with Light Blue stipe). Circuit #640 that feeds the TPS (Red with yeloow hash), and the windshiwld wiper motor Circuit #63 (Red wire).
Personally I thinking using a relay to power an electric choke is a bit of overkill, but there is really nothing wrong with it other than introducing an additional layer of complexity when iit really is not needed. Speaking of overkill, the other year I decideded to correct the electric choke wirhing on out 73 Mach 1 which is running a 750 CFM Holley carb. The prior owner had wired the Circuit #16 wire from the starter relay's "I" terminal. It :worked, eventually, and resulted in me blowing a lot of black smoke during engine warmup as the lower voltage from the ignition system's ignition coil positive terminal. After a few years of dealing with that I finaally rewired the elecric choke to be powered from the windshield wiper #63 power circuit (Red wire). I did that because I do not drive the Mach 1 when th roads are not perfectly dry, so I know I will never overload Circuit #63. I was tempted to use a relay and let Circuit #4 trigger the relay, but decided I really did not need that level of complexity. Besides, I am already using Circuit #4 to trigger a headlight relay for full time headlights ro be on in an effort to make sure other drivers see the Mach 1 - my attempt to further help prevent an accident as I never want that car to get damaged.
So,why did I say what I did was overkill? Because I video recorded my cutting over to Circuit #63 to power the electric coke. You can see how I did the rewiring by hitting my YouTube channel. The video is at:
https://www.youtube.com/watch?v=WDcskIPfLcE&t=2s
My YouTube channel is under "Gilbert Hale, and can be seen at the following link. I have all kinds of videos for vintage Mustang diagnosis and repair procedures I felt might be of value to others.
https://www.youtube.com/@gilberthale7777/featured
I hope all that helps you.
