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Hi All
My rear window demister has stopped working..
the light does not come on when the switch is pressed so i thought it may be the switch..however if i unplug the wires going from the switch to the demister 
module in the rear quarter by the jack in the back i get 12 v from the connector
and the light on the switch comes on..plug it back into the module ..light goes back off..
So i unpug the demister harness on the other side of the module (output to the actual demister heater bars) and light comes on.. plug it back in light goes off
so im assuming that its the actual demister bars that have an issue..if one of the wires have come off the demister bars it would be like a open circuit?
as tho i unplugged the plugs wouldnt it? therefor the light would come on? but it doesnt...any ideas?
when the switch is pressed so i thought it may be the switch..however if i unplug the wires going from the switch to the demister 
module in the rear quarter by the jack in the back i get 12 v from the connector
and the light on the switch comes on..plug it back into the module ..light goes back off..
So i unpug the demister harness on the other side of the module (output to the actual demister heater bars) and light comes on.. plug it back in light goes off
so im assuming that its the actual demister bars that have an issue..if one of the wires have come off the demister bars it would be like a open circuit?
as tho i unplugged the plugs wouldnt it? therefor the light would come on? but it doesnt...any ideas??

Cheers!

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The "module" in the back is a noise suppressor unit.  So, it's just going to be a capacitor (at best guess). The fault is probably in there, if it is a big ol' electro cap, it's probably popped its load all over the insides of the box.

Here's the wiring diagram. It's not rocket surgery to work out where the pixies come from and where they flow to. Put 12V direct onto the hot side of the demister bars and see if they get warm. Looks like the switch's lamp is back fed off the output that comes out of the switch and goes to the back of the car.

image.png.139b763b7327a912ca665ebbcfa8d043.png

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ive tested the wire from the switch output that goes into the noise suppressor =12v then the output  on the output side of the noise supressor =12v 

tested the hot side of the demister bars with a ohms test = closed circuit..

does any of that info help diagnose whats going on?

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4 hours ago, boomtheroom said:

tested the hot side of the demister bars with a ohms test = closed circuit

Mark up the drawing with the connection points across which you measured short circuit.

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