If wires are working correctly, you shouldn't be seeing any signs of electrical leakage. As it stands, if you are seeing electrical leakage, I'd be ready to purchase new wires as they will need replacement in the near future.
You can test some wires by doing a resistance check. Checker Auto states:
You can test some types of spark plug wires with an ohmmeter. Basically, there are three spark plug wire types, but more on that later. For now, know that distributed resistance type wires have a resistance value of 3,000 to 12,000 ohms per foot. MAG and fixed resistor spark plug wires have much lower resistance per foot. But the actual resistance per foot isn’t important. It’s the consistency of the readings between each wire that determines if the spark plug wire is good or bad. So, measure the length and resistance of each spark plug wire and write it down. Then compare the resistance values. A bad spark plug wire will have much more resistance than another wire of equal length. That’s your signal that it’s time to change spark plug wires.
There are (basically) three different types of wires:
- Distributed resistance
- Inductance (MAG)
- Fixed resistor
You can only measure the resistance on the Distributed resistance type. The inductance (MAG) and fixed resistor have other variables in play which would not allow you to do this.