From 09/2001:

WARNING: This page is about a different variant/trim than selected.

Version with rain/light sensor.

Expand two-part mirror base cover (1) by pressing from below and detach.

Fig 1: Removing Two-Part Mirror Base Cover

Courtesy of BMW OF NORTH AMERICA, INC.

Feed out two-part mirror base cover (1) and remove.

Disconnect plug connection (3).

Fig 2: Removing Rain/Light Sensor

Courtesy of BMW OF NORTH AMERICA, INC.

Press locks (1) in direction of arrow and remove rain/light sensor (2) towards bottom.

Installation:

Do not damage optical element below rain/light sensor (2).

If necessary, initialize rain/light sensor. Refer to 61 35 680 INITIALIZING RAIN SENSOR .