Hello and welcome to Just answer,
I am sending you the schematic for the defogger systme on your Impala,
Check the Batt 3 40A fuse and the defog relay for a click when the dofogger switch is pressed. These are both located in the under hood fuse block.
Let me know if you have more questions
Relay activates when button pressed. Batt3 40A fuse ohms out correctly. With relay active and 40A fused removed, 12.5 Volts present on one relay stud other at ground.
I appears that it is a harness open. Are the C1 and C2 connectors those found at the heating element? Were is the C200 connector located?
Yes C1 and C2 are at the element.
Below are the connector face and locations of C200. D6 is the element supply voltage.
C200 (40 cavities)
Body wiring harness to the I/P wiring harness, behind the right front kick panel, below the I/P fuse panel
Rear Defog Element Supply Voltage (Coupe)
Rear Defog Element Supply Voltage
Rear Defog Element Supply Voltage (Sedan)