The part the OP has in question: – the parts big end attaching to ground and wire end attaches to one of the ignition coil wires (battery or “+”, I think) – is called both a radio suppressor, a capacitor or also called a condenser.
In 1977 the official part number for the “radio suppression” ignition coil capacitor is 3501735.
Vehicles without radios did not come with this part and it is considered to be “radio” part, not an ignition system part - in the official part books. Chrysler has used this same part (not necessarily the same part number) sense before mid ‘60s to present.
I looked up the same part number for 1988 and part number is 4048646 (also called a radio noise suppressor).
Vehicles with points also have one inside of the distributer (as well as one on coil for radio), but it is to increase the lifespan of points. It is a capacitor, but for some reason the commonly used name is condenser.
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The 4 pin and 5 pin ICU’s can/will interchange.
When they were first used, they used the lower resistance half of dual ballast resistor to give higher voltage upon startup.
They found out that wasn’t necessary, so that section was bypassed completely on all newer ICU’s (and vehicles).
(The extra pin has nothing to do with the capacitor mentioned in the first post)
If you have a car with a dual ballast resistor, and car will not start until you let off of starter mode OR if starts on start mode but dies after you let off – then you have bad ballast resistor.
Back in the 70’s & 80’s, it was always a good idea to have a spare ballast, ICU and voltage regulator in your trunk.
Now days, those parts seem to be more reliable.
BudW
Picture added