The typical spark plug wire used today in some of the racecars should be a magnetic core with radially wound monel wire wrap around the core. Unfortunately quality is all over the map. Many wire sets do not follow the original French patent of using a magnetic core....problems abound when decreasing manufacturing costs. The coil wire sees more energy per time than do the individual plug wires and over time the wire condition can break down.
Higher distress happens when underhood header heat and wider spark plug gaps are applied.
An easy way to keep track of the secondary wire condition is to log (record) the resistance (Ohms) when the set is new and periodically re-test it and compare to the base log data. Another easy way is to run the engine in total darkness and look at the corona discharge at each end of each of the wires. This glowing corona discharge will grow over time and is a decent indicator of when one should consider changing wire sets.
Regards to All that like this kind of stuff,
HB2
Dissident
