Hook your voltmeter to the coil+ Crank the engine using the key. You should have "same as battery," meaning whatever the battery reads during cranking. You need AT LEAST 10V 10.5 or higher is "better."
I know this is a super old post, but thank you for this. Was having no spark issues in my 72 Dart Custom 225ci.
I was thinking I had a bad coil, but I found this thread and followed this instruction and found I only had 8.3v going to the coil. It ended up being caused by a bad ground at the module.
Cleaned everything up and now I’m getting 10.6v to the coil and spark is back and car is running great. Drove 40 miles today at 75-80mph without issue.