I found this quote from 2023 in another thread about Pertronix needing R sparkplugs, or not; and why Pertronix has changed to requiring carbon wires vs. copper core with their newer units. Because this was a Tractor thread, I suspect in wet applications, especially with older solid core wires there were 'spike' problems. In any case, I'm going to contact Bud's next week and ask about my 2015 install whether they suggest switching back to the WR7DC plugs they installed and tuned with the then new Pertronix.
"We're a Pertronix dealer and a few years back, Pertronix was trying to figure out why their modules were blowing out especially in Tractor applications. According to their bulletin back then, they finally figured out with quite a bit of R&D if using a solid core wire, a stray spike could blow the module out. This is when the bulletin said that anytime selling an E.I. to a customer, make sure the vehicle is NOT equipped with solid core wires. Make sure the customer installs carbon core wires which will stop the stray spikes the solid core wire can give off especially in humid or wet weather/days. From what I understand, since using the carbon core wires, Pertronix E.I. failures were cut way down big time. You don't need to run resistor plugs with the carbon wires.... HTH
Steve@B&B"