Originally Posted by Kira
Caveat: Just because a set of wires is clad in nice, new silicone compound rubber doesn't mean the inwards are quality.
Buy quality (you know that, just sayin')
Have you done the "Open the hood on a moist night with the engine running" test to check for dancing sparks?
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I've been disappointed in Denso wires, they are not made by Denso themselves - they aren't getting them from Seiwa or one of the Japanese plug wire suppliers(or even Prestolite). Bosch disappoints me as well, even where they are OEM. It seems like getting wires at the dealer or using NGK/Motorcraft/Delco(if your car has them available) is the only way to get good wires.
The open hood on a dark night/garage test seems to work pretty well to diagnose wires besides feel and looks. You will need a megger to test the insulation otherwise.