[header] How to test spark plug wires [title] Check for symptoms. [step] Defective spark plug wire leave tell-tale signs of their deterioration, including : [substeps] An erratic idle engine misfire radio interference decreased fuel mileage failed emissions tests due to elevated hydrocarbon emissions or a fault code indicating cylinder misfire. Check engine light [title] Inspect the wires. 
[step] Use a flashlight or an area with good lighting to perform a visual inspection of the spark plug wires. [substeps] Look for physical damage to the wires or boots such as cuts and scorch marks.