All about U5
Low voltage connection
Most pencil coils have a low voltage connector with three pins: Ground, battery voltage, ignition signal.
Some only have two pins: Battery voltage, ignition signal
Versions with integrated ignition module may have a different layout.
Depending on the angle at which it is viewed, this connection is the end of the secondary coil or the connection point to the spark plug. Through this connection, the ignition voltage travels to the spark plug, where a spark-over occurs.
U5 category pencil coils are positioned directly on the spark plugs. An ignition cable is not required.