Light Control Rheostat
WARNING: This page is about a different car, the 2003 Lexus GS 430, 2003 Lexus GS 300, 2002 Lexus GS 430, and 2002 Lexus GS 300. However, it is still accessible from the selected car via links, so may be relevant.
Gradually turn the rheostat knob from the bright side to dark side and check that the resistance decreases from 10 k ohms to 0 ohms between terminal Nos. 4 and 5 (rheostat knob turned to clockwise). See Fig 1. If the operation is not as specified, replace the rheostat light control. See INSTRUMENT PANEL under REMOVAL & INSTALLATION.