The power pack or switchbox is the control center of a capacitive discharge ignition system. Its job is twofold. First, it stores electrical energy produced by the stator. Second, it releases that stored energy at exactly the right moment to fire the correct cylinder.
The timing signal that tells the power pack or switchbox when to fire comes from the trigger / timerbase. As the engine turns, the trigger senses flywheel position and sends a signal telling the pack which cylinder is ready for spark. The pack then dumps its stored energy into the proper ignition coil, and the coil boosts that energy into the high voltage needed at the spark plug.
This is why the pack is so important. Even if the stator, trigger, and coils are all good, the engine will not fire correctly if the power pack or switchbox cannot store or release energy properly.
A failing pack can cause a wide range of problems. It may lose spark on one cylinder, lose spark on multiple cylinders, break down only when hot, misfire at higher rpm, or cause an intermittent no-start condition. Sometimes the motor will start and run, but fall flat under load because the pack is no longer releasing strong, consistent spark.
Power packs and switchboxes can also be damaged by problems elsewhere in the ignition system. A shorted stator, bad trigger, poor grounds, weak battery connections on battery-powered systems, incorrect bias circuit conditions on certain multi-pack applications, or improper wiring can all damage the pack or make it appear bad when the real problem is elsewhere.
On some engines, especially multi-cylinder models, it is important that all related ignition components be tested carefully before replacing one pack. In dual-pack systems, an old failing pack can sometimes damage a new one if other ignition issues are left unresolved.
In simple terms, the flywheel and stator create the energy, the trigger tells the system when to fire, the power pack or switchbox stores and releases that energy, and the coil sends it on to the spark plug.
