How can a bad plug wire destroy good coil?

A bad plug wire can destroy a good coil by causing the coil to overheat. When a plug wire is bad, it can create a high resistance connection between the coil and the spark plug. This high resistance can cause the coil to work harder than it needs to in order to produce a spark, which can cause the coil to overheat and eventually fail.

In addition, a bad plug wire can also cause the coil to arc, which can further damage the coil. Arcing occurs when the spark jumps from the coil to the spark plug instead of traveling through the plug wire. This can create a lot of heat and can quickly damage the coil.

Therefore, it is important to replace bad plug wires as soon as possible in order to prevent them from damaging the coil.