When we have a card to replace the igniter plugs, we carefully take the old ones out, by first you must disconnect the electrode and ground it to the case because, they don't forgive if you zap it on your finger or hand. YOUR DEAD! (Usually, by the time you get to them, they disipitate after some ten minutes or so after engine shut down, and which by the time the plane is towed in the hanger, its been long stopped running but I wouldn't put my life on it. Ground it anyway.) Then you put the new igniter in place. Two per engine on the ones we work on. Little anti-sieze and torque it down. Now comes the test. PROJECT IGNITE. We call it a POP CHECK. You can hear the spark plugs clicking. That means, FIRE IN THE HOLE! You did the job right.