Spark plug wires are pretty tough; they don't need to get replaced that often since it has no moving parts. However, it’s still a good idea to test the wires that carry the voltage necessary to run your engine.
Step 1- Inspect the Wires
The insulation (rubber coating outside the wire) may break and cause arcing. Run a damp rag from end to end and feel for any break. Bend and check the wires for brittleness and cracks.
Step 2 - Check for Looseness
Remove and reinstall the spark plug wires. Inspect both ends for cracks. If it comes off easily, replace it.
Step 3 - Observe for Shorts and Voltage Leaks
During the night, pop the hood and with the engine running, look for little flashes or some popping sound near the wires and distributor cap. If you see some sparks, your spark plug wires need to be replaced.
Step 4 - Measure the Resistance
Using a multimeter, measure resistance between two points of the spark plug wires. Take off both ends and measure the resistance between them. Normal spark plug wires is 10-15 thousand ohms per foot of cable. Lower values are much better. If resistance is higher than this, wires must be replaced. If the meter indicates an open circuit condition, then replace wire.