Switch Assembly
WARNING: This page is about a different car, the 2005 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.
Be sure there is continuity between the terminals S and M, and between terminal S and ground. Use a circuit tester (set in "ohm").
Also check to be sure there is no continuity between terminal M and B.
Terminal/Specified resistance:
S - M/Less than 1ohm
S - Ground/Less than 1ohm
M - B/More than 1 Mohm