So, what is it exactly that dictates which ICM you use? Did a body swap, only difference in anything is that I kept the engine in the frame with its distributor. Changed ICM and it now runs. So, leaves me to believe that they are matched to distributor. Would this be an accurate guess?

 

There are several part numbers for different years but I haven't found any that don't work on the Fords as well as the Jeeps I've had.

That said I've always run the proper one for the application because I figured there must be minor differences. whether this is true or not I don't know.

 

The only differences were the wiring harness accompanying the body. This is usually to accommodate some slight internal difference in the different modules and to keep people from swapping the wrong one in where it should not be.
The distributors were all the same for all years Dura Spark. Other than external visual differences, the 3-wire connector and pin orientation were identical. So ALL Dura Spark modules can be triggered by ALL Dura Spark distributors.
The differences were many with regard to the modules though. And even two or three different ignition coils if I remember. Probably 9 or 10 different modules were used over the years. Differences were for things like differing emissions requirements (CA vs the FED at that point), high-altitude vs normal, and just the generational changes that occurred as Ford was fine-tuning the performance and features, as well as fixing faults with them. I forget which color it was, but NumberDummy has stated many times that there was at least one module that was practically a guarantee of failure. The old Brown, or Red, or maybe Yellow grommet modules. I forget.
But only a few of them over the years were able to utilize the same wiring harness connections. That's the big difference to determine what a given truck will use, or whether you have to reconfigure the wiring to get a particular module to work with your system.

So they will all work with the distributor, and will all fire the coil, if not all reliably. But your wiring connections will vary.
What color was your old module, and what color is the new one? And by color I mean the wire strain relief where the wires come out of the base of the module. The color of that "grommet" is how they are first identified.

Bottom line is yours works, and that's a good thing!

Paul

 

Modules have a colored plastic grommet adjacent to where the wires feed out used to ID them. The most common module used 1976/79:

1U2Z-12A199-AA (replaced D6AZ-12A199-A & B; D8VZ-12A199-A; D9VZ-12A199-A) .. Ignition Module - Blue Grommet (Motorcraft DY-893)

1976/90's myriad FoMoCo vehicles.

1978/79 FoMoCo vehicles sold in high altitudes (5,000'+) with 300 I-6 (F100) or 302's have a module with either a Brown or Yellow Grommet.

If the module is an original Motorcraft, it will have ID numbers embossed on it, similar to: D9VE-12A199-AA

 

Thanks. Thought it strange that both blue, would only work on rigs they were in but wouldn’t swap. My problem is fixed bit wondered what the real difference between the colors was. ND, sounds like maybe a tune, or spark duration/ intensity sort of speaking? I’m fairly savvy on these rigs, was just something that I always wondered about, what the actual difference was.