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Structure and inner electrical connection

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The ignition coil operates according to the principle of a transformer. 2 coils are placed onto a shared ferric core. The primary coil consists of a thick wire with just a few windings. One end of the coil is attached to the positive terminal (terminal 15) of the vehicle voltage via the load-shedding relay terminal 15. The other end (terminal 1) is connected to the ignition output stage, which can use it to switch the primary current. The secondary coil consists of thin wire with many windings.

Fig 1: Coil And Spark Plug - Circuit Diagram
G09909865Courtesy of BMW OF NORTH AMERICA, INC.
Item Explanation
1 Primary coil
2 Secondary coil
3 Spark plug
PIN REFERENCE

Pin Explanation
Terminal 15 Voltage supply (via load-shedding relay, terminal 15)
SIG Ignition signal, terminal 1
Kl. 4a Earth connection