Electronic Back Light (EBL) relay
WARNING: This page is about a different car, the 2004 Dodge Grand Caravan, 2004 Dodge Caravan, and 2004 Chrysler Town & Country. However, it is still accessible from the selected car via links, so may be relevant.
The rear defrost switch is part of the Automatic Temperature Control or A/C-Heater Control Module (Manual Temp). When the ignition switch is in the RUN position and the rear defrost switch is turned on, the ATC or A/C-Heater Control Module sends a PCI Bus message to the FCM. The EBL run only relay is then powered through low side control on pin 31 of the FCM. The relay provides the high side to the rear window defrost grid, and ground is attached to the vehicle body. The FCM will only allow the rear defrost to operate in the RUN position. This circuit is electronically controlled and continuously monitored for malfunctions.