WARNING: This page is about a different car, the 2010 BMW 550i, 2009 BMW 550i, and 2008 BMW 550i. However, it is still accessible from the selected car via links, so may be relevant.
ELECTRIC AUXILIARY HEATER - TIGHTENING TORQUES SPECIFICATION
Type
Thread
Tightening specification
Measure
1AZ Battery positive and negative leads to auxiliary heater