Circuit Description
WARNING: This page is about a different car, the 2003 Lexus IS 300 and 2002 Lexus IS 300. However, it is still accessible from the selected car via links, so may be relevant.
The taillight relay will be ON by operating the taillight switch. The transistor which activates the taillight relay has 2 sorts: one activates by the taillight switch for fail safe and the other activates by the CPU. For circuit diagram, see Fig 1.