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

Any time a wire exhibits physical damage either to the wire or the boots, such as a cut, grooves or marks from chafing or scorch marks from burning, the wire should be replaced as preventative maintenance.

Additionally, some wires fail from the inside, due to a breakdown of their insulation materials. Wires should always be inspected and tested whenever a rough or erratic idle is present, poor acceleration is noticed, a decrease in fuel mileage is experienced or a vehicle fails an emissions test due to high hydrocarbon emissions or cylinder misfire fault code.

Wires should be replaced if their resistance exceeds the OEM specification for their specific application. Wires should always be replaced as a set due to the unpredictablility of the internal condition of each individual wire.