Rear Defrost Issues

[shamrok]

Switch is good, I've verified power to the wires at the defroster end is good. Grounds to the window are good. What specifically about the rear defrost would fail the whole thing? I've had cars in the past where you could tell some of the elements had failed, but everything? I'd replace, but of course it's 4 figures to replace and I want to eliminate something obvious if I can.

[Tea Tray]

In looking at the Bentley diagram for an ‘84 Carrera and referring to wires/terminals on the defrost relay in the engine comp:
The RD/WT wire on the relay, #87 goes to 1 heating element in the glass.
The RD/BK wire on the relay, # 87a goes to 2 heating elements in the glass.
The BK wire on the relay, #86 goes to the outside mirror heaters.
Try removing the three above wires and measure resistance to ground. I don’t know the wattage but if you share the resistance measured, it’s an easy calculation.

Bentley 970-53