All about U1
Depending on the angle at which it is viewed, this connection is the end of the secondary coil or the connection point to the distributor and/or spark plug. Through this connection, the ignition voltage travels to the distributor and from there via the individual ignition wires to the spark plugs, where a spark-over occurs.
Terminals 1 and 15
Low-voltage connections: minus / ignition signal / Trigger(1) and battery power / 12V (15) terminals. The ignition coil is supplied with current through these terminals.
Block coils (some with integrated ignition module) like U1001 often combine the low voltage connections in a compact connector. (Pin assignment: Battery voltage, ground (GND), ignition signal (Trig) from engine control module)