Wiring Suggestion/Help

Mattax said

Piggyback at the ballast resistor on the ignition run side. (Dark Blue J2 wire)
View attachment 1716215240
That's power for ECU and connects to the top position of the ECU connector.
View attachment 1716215242

Then a ring terminal is needed on the wire from the ECU connector that will connect the coil negative to ground when the ECU is triggered by the pulse from the distributor.
That's about it.
Make sure the ECU bousing is grounded to the sheetmetal.
For a long time, Mopar recommended using a solid state voltage regulator when converting to ECU.
These days many replacement regulators (such as the one sold by FBO on ebay) are transistorized so that allows you to keep field circuit wiring as it is.

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First of all, thank for providing all the information. Sadly, I am 100% electrically illiterate but the shop doing the build isn't and my elctrical engineer neighbor is highly proficient, though I can never understand him when he talks electrical stuff. I'll inquire about this things over the next two days. Learned that the '74 slant 6 from the Duster did have AC on it, so I need to call the guy I bought it from to see if he still has the orignal compressor and bracket. If he does, then my hope is that we can use that to eliminate my aftermarket issue there and use the mechanical fan with a standard radiator. Then the question is whether we can/should go back to non-electic ignition. This car will be driven a fair amount (e.g. not just car events), so looking to accomplish a restomod to it. Thanks again and keep the advice and experiences comin'