I was asked the other day to look at a set of spark plug wires to see if there was a problem with them. Well, it’s not very easy to just visually inspect spark plug wires for problems.
I Mean, as long as the wire is intact, not cut; the spark is not jumping out of the wire from a knick or cut or anything obvious….it will just appear to be a normal spark plug wire. What I can tell you is that spark plug wires have numbers stamped on them from the factory. 
When I see numbers stamped on spark plug wires it’s a pretty good assumption that they are the original spark plug wires. If you are experiencing an engine misfire and suspect either spark plugs or spark plug wires as the culprits I would replace the plug wires if you see these numbers stamped on the wire and they have more than 50,000 miles on them….replace them.
Blessings,
Austin Davis