Spark plug wires are designed to carry the electrical voltage from the ignition system to the spark plug. They are designed to have very low resistance so the maximum amount of energy is transferred. This transfer of energy can be interrupted by several factors:
Improper connections between the wire set and cap can cause damage similar to this. The voltage actually arced between the wire set and the cap and eventually burned through the wire set and rotor, destroying both. During installation, always make sure all connections are secure.
Improperly designed wire sets can cause dangerous problems including interference with the throttle cable linkage, causing the gas pedal to stay open, or resting on the exhaust manifold, which would cause the wire to burn. In addition, if wire sets are not installed correctly problems can occur. When installing wire sets, make sure the connection between the spark plug and the cap is secure to avoid ignition problems. See Photos 1 and 2 to see damage caused from improper installation of wire sets.
Spark plug problems
If combustion gases leak past the spark plug, the spark plug wires can become unconnected from the spark plug terminal due to the increased pressure. Or, the opposite effect could happen and the gases can cause the spark plug and the wire terminal to corrode and fuse together.
If moisture becomes trapped in the spark plug hole or between the plug and the wire, it can cause arcing. This will cause permanent damage to the spark plug wires and possibly the spark plug as well.
Excessive heat from exhaust headers
Routing spark plug wires in areas with excessive heat can destroy the silicone insulation. To prevent this, all Bosch spark plug wire sets are designed specifically for each application to ensure wires are out of harm’s way.
Spark plug wires need to be removed carefully. When removing the wire, do not pull on the wire, but instead grasp the plug boot firmly and gently remove. Make sure the engine is cold. This will prevent the connectors from becoming loose.
Courtesy of Bosch.