How do I check/trouble shoot spark plug wires and distributor cap? I think I have a bad wire or plug (engine is running like it's a cylinder short.)

ADN;

Checking for high voltage leakage external to ignition components is very effective at night as Chris suggests.

You can unconnect, one at a time, plug wires and plug them into a spare plug which you then lay on the valve cover. This allows checking for spark with the least intrusion on the system.

Also, if engine starts on three and smooths out after warming, start it, and shut off after 30 secs. or so and (carefully)feel for heat at exhaust...this will locate the nonfiring cylinder...try replacing plug first and try starting again, if no improvement, check plug wire and cap, especially at problem cylinder connections.

Good Hunting

Also, while the engine is idling, disconnect plug wires one at a time until you find the one that has little effect upon its removal. You can then swap plugs and wires with neighboring cylinders to further pin point the problem.

/// Definitely count the cylinders. Running a cylinder short will definitely effect performance.

When in doubt replace. Use an old spark plug clipped to engine ground. Attach each plug wire (in turn) to this substitute. Bump the engine over while the ignition is on. Observe the spark.

Pull the plugs and observe the condition of each. Almost every car manual has a page on engine diagnosis through sparkplug condition. It is possible that you have a shorted plug (look for bridging at the tip) or some other damage to the plugs.

Run the engine in the dark and look for sparks from old wires.

Pull the distributor cap and inspect the cap and points (if you do not have added electronic ignition). Be careful to check the ground path for the capacitor. If the ground for the capacitor is bad the points will arc and burn and the car will perform as if the timing is off.