Circuit Description
WARNING: This page is about a different car, the 2002 Lexus SC 430. However, it is still accessible from the selected car via links, so may be relevant.
Signal via the rear defogger switch is transmitted multiply to the luggage room J/B from the air conditioning amplifier, then the luggage room J/B outputs it to the defogger relay.
NOTE:
Rear window defogger system has a function with a large-scale body multiplex communication. First of all, inspect the communication function according to "how to proceed with troubleshooting", and check that no malfunction exists in the communication system. Then proceed with the troubleshooting.