You do know that if you are using a 1975 Factory Service Manual, as it appears you are, then it has procedures to test every single aspect of the ignition system. ECU, ballast, pick-up module in the distributor, ignition coil itself. All of it. That's what the techs originally used at the dealership.
Ive run through that entire section of the manual so far and run all the tests it says to run with the exception of the "testing ground circuit" because it says to check the number 5 pin on the ECU which I cannot due because there is no longer a 5th pin since they've all be swapped to the 4 pin design. Cavities number 1,2,3 on the ecu connector are all right at the 1volt tolerance level as it says in the book and the resistance between cavities 4 and 5 is 280 ohms, which is within the tolerances the book gives. I event went to the passenger side and disconnected the plug on the distributor and tested that way as well and still got 280 ohms. The last thing i have to do in the testing section is to remove the power cable from the coil to the distributor cap and hold 3/16" away from engine and turn it over to see if it has an arch( basically the same thing one of the previous member recommended I do).
Have you VERIFIED there is no spark at the plugs? That means remove one, lay it against a ground and then crank the engine over. You could have something as simple as a corroded terminal in the cap or a broken coil wire. I'm going to be retesting them since I've been making all the correction to the hack job wiring that was done by PO's.
Accel coils are junk. You can get the correct replacement ignition coil for about $19 in stock at pretty much any Autozone on the planet. Ignore the drama about the "ECU might have a ballast in it blah blah". Whether it does or not Mopar spec'd what ballast and what coil to use so put it back stock.
Ive tried starting the car with the original coil that came with the car when i bought it and the new accel coil with the exact same results so i don't see it being an issue with the coil.
I think i mentioned this in another thread you started but the ballast supplies two separate voltages at two separate times:
Cranking voltage which is supplied to the coil when the key is in START. That's full 12V to help the engine start faster. Even when running a jumper wire straight from the battery to the + coil terminal the car still wouldnt start.
Running voltage which is resisted down to about 6-7V at the coil. That's because the coil tends to overheat and fail at full voltage. That voltage is supplied when the key is in ON position.
That's why when the run side of the ballast fails, since it does all the work, the engine starts as long as the key is in START and sending that full 12v to the coil. When I measured the voltage from the terminal and used a screwdriver to jumper the starter relay there was no difference in the voltage at the coil + terminal, so it never switched to the 12V full power voltage that your referring to. Now that i think about it i may be wrong in doing so and actually need someone to turn the key while checking for the switchover in voltage because im not sure if it would actually send the 12v to the coil without the key being physically turned. I haven't dug that deep yet.
Here's a challenge:
Imagine it's 1979 and you are a newer line tech at FABO Chrysler-Plymouth, and you just had a 4yo '75 Dart come in with a no-start. It's assigned to you to repair. The customer needs their car back as soon as possible because it's their only car.
Every hour you spend working on that car not only charges the customer the hourly labor rate, but keeps you from taking on other jobs. Not only that, but the customer is on the hook for any replacement parts since that car is now out of warranty.
So, what do you do? Do you take guesses and try different parts, all of which are billed to the customer. Do you fart around wasting diagnostic time?
Or do you utilize the tools at hand, namely the proper electrical test equipment( a spark tester and an electrical meter) plus the FSM with it's detailed diagnostic instructions to quickly isolate the real problem, repair it and get the car back to the customer without excessive labor and part costs, which they would most certainly balk at paying?
Being a divorced single father with custody of my two kids, I don't have tons of money just laying around, and I don't like throwing money at things in hopes that I eventually replace the right part. If I did I would have bought an entirely new electrical system or paid someone else to do it instead of digging through the diagrams and trying to trace things down myself. If I didn't have spinal surgery 3 weeks ago trust me this would have been fixed long ago. I do as much as my recovering neck can handle at a time before I'm forced back in the house.
:)