This one bites a lot of people as the coil connection on the cap attracts carbon over time. At the bottom of the boot you will notice a carbon ring that covers the circumference of the center connection. The spark jumps directly to the black plastic insulator therefore giving electrons what they love, the shortest path to ground! A spray bottle filled with water is a valuable secondary ignition system tester........simply spritz (not drown) a little water over the entire system and listen for the snap! If the cap connection is really bad the engine will die instantly once it is sprayed.

I knew a 420 that suffered with an extremely hard cold start issue, after the initial start it would be fine ther rest of the day.

A dist cap cured that one..........................................................