Spark plugs and wires replacement

It is real common to have one ignition coil fire two spark plugs at the same time, one on the compression strike and one on the exhaust stroke. The one on the exhaust stroke is referred to as the "waste" spark. Three of your spark plugs use the coil-on-plug ignition coil design so they do not use spark plug wires. Most manufacturers use six ignition coils, but Toyota saved a few bucks by using only three. The mating cylinder uses a spark plug wire to carry the spark. The only drawback is when a coil fails. You will be driving on four cylinders instead of five. The advantage is you only spend half as much on wires.