Disconnect the ground wire from the battery.
Remove the protective cap from the ignition coil.
Disconnect the electrical wires from the ignition coil.
If the "arrow" plug is pressed out, replace the ignition coil.
Check the resistance of the primary winding. To do this, connect an ohmmeter to terminal 1 and terminal 15.
Check the resistance of the secondary winding. To do this, connect an ohmmeter to terminal 15 and terminal 4 (see table 1).
Table 1
Connect the electrical wires to the ignition coil.
Place the cap on the ignition coil.
Connect the ground wire to the battery.
Attention: When replacing the ignition coil, do not install the coil from the old contact ignition system under any circumstances. This may damage the control unit.
(Information taken from this resource: BMWman)