While most newer vehicles use a coil-on-plug (COP) design for ignition, older vehicles still need plug wires to get the spark from the distributor to the plugs. The spark plugs themselves can serve anywhere from 30K to 100K miles before needing replacement, but the wires can degrade and crack much sooner.
Changing plugs and plug wires is an easy job (just remember to replace one plug wire at a time to preserve proper firing order). Shop Advance for spark plugs and plug wires from top brands like Carquest, ACDelco, DENSO, Ford Motorcraft, Champion, NGK and Autolite.
The distributor was replaced by a distributor-less ignition system (DIS) that uses a computer, camshaft position sensor and crankshaft position sensor to determine spark timing. The DIS system uses one or several coil packs to generate spark. On vehicles with waste-spark DIS, one ignition coil pack will fire two spark plugs.
Today the most common DIS ignition system is the coil-on-plug (COP) ignition system. Each cylinder has a dedicated ignition coil for each spark plug; most often with the ignition coil sitting directly above the spark plug. Plug wires have a finite service life and tend to 'leak' current when they get greasy, dried-out or generally worn.
Here's a quick way to see if your spark plug wires are getting to the end of their lifespan: drive to a very dark spot at night, pop the hood with the engine running, and use a spray bottle to lightly spray a mist of water up and down the plug wires. If they're starting to fail, you'll be able to see arcing between wires.
When replacing plug wires, just be sure to replace only one plug wire at a time and match that wire's length precisely against the old wire. That way you can be sure you're maintaining the original firing order of the engine.