The speed of the fan blower is controlled through two types of setups on the BMW E34:
the final stage unit (older E34s) also called "the sword" because of its look ($140) or the blower series resistance ($30).
click once more here
Above pic is from a left hand drive E32, but location of sword is same.
Also have a look here, it refers to the microfilter replacement (only installed from 06/1990 , no earlier models have it) on a LHD E32 car, but the pics are good and show you the 'sword', same location on an E34:
click here