WARNING: This page is about a different car, the 2010 BMW 135i, 2009 BMW 135i, and 2008 BMW 135i. However, it is still accessible from the selected car via links, so may be relevant.
ELECTRIC AUXILIARY HEATER - TORQUES SPECIFICATION TABLE
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Type
thread
Tightening Specification
Measure
1AZ Battery positive and negative leads to auxiliary heater