Contour Enthusiasts Group Archives Forums Modifications Duratec Maintenance Spark Plug Questions (Arcing)

You've got the whole insulation/resistance thingy crossed up here.
Diameter is related to the resistance to voltage breakdown. THe thicker the insulation the less radio interference and spark bleed you get through the wire.

I once watched a cheap set of plug wires on a middle 1980's HEI ignition system in the dark while the engine ran.
They looked like a science fiction movie as the the bluish sparks bled out into the surrounding area around the wires and to each other in the loom. Bled is the best word I can describe it. It was amazing as the wires were cheap no-name brand but were brand new.