From the wiring CD:
Safety battery terminal (battery isolation)

To reduce the risk of fire in the event of a frontal impact, the firing circuit for battery isolation is also activated when the airbag is triggered.

In this case, a gas generator (safety battery terminal) isolates the heavy-current lead (terminal 30) from the battery to the starting motor/alternator.

E46 4-cylinder model left-hand drive

Because no increased risk of fire can be ascertained when the battery is installed in the engine compartment, the safety battery terminal will be omitted as of March 2002 (03/2002) from all E46 LHD models with 4-cylinder engines.

You would need to patch a standard battery terminal into the positive battery cable to get around this feature.