Verification, please?
Not sure why you say 'almost'. We wrote the exact same thing, unless from what you write here
and
I think I misunderstood. You were asking about the single resistor arrangement....and I was describing the dual resistor arrangement, hence my reference to the '73 wiring.
I said, 'Almost' not because anything you said is incorrect, but because part of what you wrote does not apply to the question.
Re:
IIRC, when I was looking at a '73 FSM, the Ignition on Start feeds the ECU pin through the 0.5 Ohm resistor.
I don't know why they used two pins but one possibility is they are joined internally.
In which case, during Start voltage is reduced from roughly 11 to 12 Volts by the 1/2 ohm resistor.
During Run, voltage is reduced from roughly 14 Volts by the 5 ohm resistor.
Just a guess.
Yes. On Start, the ECU is fed through the coil compensating ohm resistor.
This part, 'During run, voltage is reduced...by the 5 ohm resistor' is true for the 5-pin ECU, but is not pertinent to my question.
An aside: The lower supply voltage via the 5ohm part of the 4-pin ballast used in the 5-pin ECU is still required in the 4-pin ECUs, but is developed internally. On a Standard LX101 (a real one) you can see a big wire-wound resistor sticking out of the potting. No reason for a large component of that type in an electronic assembly unless it is being used as a voltage divider for some power hungry device.
I posted the 2-pin ballast resistor pic to indicate that the 5-pin ECU isn't relevant. Yes, that happens to be in my car, and I originally had a 5-pin ECU. Not relevant.
I am questioning why they thought it necessary to bypass the compensating resistor for coil+ on Start, but also reduced the voltage to the ECU during Start. I could understand full voltage to the ECU during start (battery voltage is lower), and compensated voltage during Run (alternator voltage is higher) but that is the opposite of what was done.
Usually, what seems odd in a wiring harness does make sense and it was engineered that way for a reason, it's just that I don't understand the whys and wherefores about it.
MSD reference was a past tense sentence. It quit some years ago.The use of the MSD is one reason the wiring in the ballast area is not as clean as it should be. I've been running no ballast and a Chrysler 'style' ECU for years. What coils do or with an uncompensated coil+ isn't the issue.
The main point of this post is about the ECU power feed on pin-1: Why reduce it on Start?
