Can someone educate me on the voltage requirements that the "Orange Box" ignition receives during cranking? Is it a full 12 volts only during cranking and then the voltage gets reduced somewhere to a different voltage after the engine is running? Or is it always 12 volts when cranking and running?
Thanks for any information offered.

It get's whatever the battery can supply after the starter hogs the current which in turn drops the available voltage. Ideally 10.5 + volts but there can be a lot of variables affecting that # both directions. I have seen them function intermittently on ~ 8V as they were mis-wired at the ballast.
Once running it should get full alternator V which should be 13.8-14.2. But once again, variables can enter due to connections, wiring grounds etc.

Thanks TJB !!

That information helps me a lot. I now understand the overall voltage function of the ECU.

In this day&age, not hard to obtain a schematic of the circuit for these older but very simple circuits.

The mopar instructions have a diagram and instructions. The ECU get's run voltage. The coil still goes through a ballast and get's start voltage at ignition, then drops via the ballast resistor in run. The ECU controls the coil charge/interuption.

That is Mopar and ECU have internal resistors as ballast. After markets may have additional controls that can eliminate the ballast.

But you asked about orange box so it is wired to run side of ballast.

Talking just about the sources and not about its actual voltage requirements or how handles the power, no matter if 4 or 5 pins Modules:

The ECU is normally sourced from the RUN (ign1) circuit blue wire, just before the ballast. On 5 pins module, it also gets a complementary voltage (for whatever reason) throught the secondary resistor (4,5-5 ohms) on ballast.

But when cranking, the RUN circuit voltage is cut by the ign switch and sources the straight batt voltage throught the Ign2 circuit brown wire. Since this circuit is still spliced into the ign circuit AFTER the ballast to feed the coil with full batt voltage, the RUN circuit keeps hot but with the voltage decay caused by the ballast. You can see this when cranking, how the brake light on cluster (and oil light if equipped) dimms our since it is spliced into the RUN circuit. If 5 pins ECU, the decayed voltage also pass throught the secondary resistor back to the ECU so is doubling the resistors path to the 5th pin.

So which voltage gets the ECU on these two stages? Aprox the same than the cluster brake (and oil) light.

How much is the voltage? I have learnt that depending on engine bay temperature too, since ballast is affected and influenced by it, but TIPICALLY the voltage decay runs anywhere between 5 and 9 volts to the coil, soooo this voltage rate will be the one running to the ECU main source depending on temp while cranking.

Engine RPMs also changes the voltage rate to the coil throught the ballast (because will heat the resistor of course so is one more temp affection) BUT, this is not an stage to be considered while cranking to the ECU.

If you are worried about the back-fed cranking power to the ECU, you can put a diode across the ballast resistor. Since this back feeds the ECU, Voltage Regulator, Alternator Field, and what ever else is connected to the Ignition 1 circuit, the diode should be able to handle several Amps.
Thinking something like the 15SQ045?
https://www.smc-diodes.com/propdf/15SQ045%20N1007%20REV.C.pdf

Pretty sure that would do nothing useful. A diode is the electrical equivalent of a one way valve, so you either bypass the ballast all the time or you never bypass it, depending on how you install it. In the factory setup the ballast is bypassed in crank mode in order to give full voltage to the coil and allow it to fire. The reason for this is that during cranking system voltage drops and if you fed it thru the ballast as well the coil might not be able to make a sufficient spark.

And they had to account for cold weather start, poor starting mixture, etc.... Are there 2 questions here, voltage to operate ECU and voltage that passes through to coil? Early system used 2 power feeds, one to coil via transistor, and the second via the 5 ohm resistor to current limit to the ECU control circuit. Later ECU did this via an internal resistor and also have a power conditioning circuit to give the ECU a clean voltage to operate and accurately see the pulses of the distributor pickup.

Good question as am getting a bit confused myself
Myself, I have always supplied FULL battery V to the ECU when in the start or run position.
I've also run full V to the coil but only while starting. I believe I have the old documentation around here somewhere i will look and post later if I find it.

I had a customer 15-20 years back that had been to several shops with an random hot start issue. His start power to the ECU was wired through the ballast. I moved it to battery V and the issue went away. he said he wasn't convinced as the issue had plagued the car since he bought it 2 years earlier. Every time I saw him for the next 3 or so years I would ask if it had failed to start yet and he woulld say no, after the first year or so, I would get a f you look

A related question that I ASSumed but never verified is does the ignition switch "RUN" position/circuit go "OPEN" in the start position ?

In run the ecu gets full voltage.

the run and start position get voltage at the same time.
that way, as the car starts and the start circuit is disabled, the run circuit is uninterrupted so there will be no "burp" in the ignition system.

actually… no. Ignition switch cuts ign1 when Ign2 is activated. But both lines are allways hot (at diff voltage levels) as far both are conected to ballast.

What it could be true is we could get a small overlapping between Ign1 and Ign2 when switch between them. Never have checked really for that.