>>>*Congrats! You have discovered a test I have used for decades.

Those nice blue lights under the hood really aren't there to help you find the keys to the house in the dark....*LOL**..

*The price of a set of wires doesn't reflect the quality but sometimes the fault lies not completely in the wires themselves.

Simple ground faults can cause one heck of a lot of drivability troubles with modern engine systems. Be sure to check all the plugs to be sure they are properly gapped and correctly torqued down, use a spot of heat sink grease at the connections, also go over all of the engine ground straps.

I remember finding one of those blue lights on a mid 60's Ford at the throttle linkage right where it connected to the carb throttle arm. That turned out to be the cause of a pesky hesitation and mild backfire I had been chasing for a few days.

The grommet was worn enough that with a bad engine ground strap the voltage simply found it's own path.

Even with brand new wires, voltage will follow the path of least resistance. The only reason a spark plug fires is because it is forced to if the voltage has no place else to go. Therefore the spark jumps the gap, against the resistance of the plug gap. If it can find another easier gap, it will jump at that point, or perhaps "leak" would be a better term....*EB