Jimmy,
The simple answer is, OH YEAH, power packs go bad all the time! Often, loose or corroded wire connectors or battery cables are the start of the problem. The arc or resistance damage the rectifier/voltage regulator and the CDI.
I strongly recommend that you scrape and wire brush your connectors until they are shiny metal and re-test, if you haven't already. Sometimes a film forms on connectors that is pretty transparent, but it still interferes with conductivity.
Like Pappy, I work on a lot of them, and what he told you is exactly the proper sequence. If you already verified that the black/yellow wire is not broken, but it still doesn't shut the motor off, your CDI may be bad. That is likely your problem, but there are other possibilities.
You can melt the potting and chase it down inside if you are that adventurous, but it's easier to just order a power pack off Amazon, swap them out and go use the boat.
Here is the parts diagram for your motor:
https://www.boats.net/catalog/johnson/outboard/25hp/j25elcne-1982/magneto
Part 37 is the CDI power pack. This is the OEM version. On those little motors, I have used other brands with great success. Here is the CDI version at about half price:
https://www.amazon.com/CDI-Electronics-113-2453-Evinrude-1977-1984/dp/B012RQHB10
Don't be too sensitive on online forums. Text often doesn't come across as intended.
I hope you get your motor fixed and enjoy your summer.