OK, after another frosty morning, I decided to tackle my broken rear
defroster. There's power at the fuse panel and the yellow indicator
comes on when I press the defrost button. So I popped off the C pillar
trim and see a strange translucent blue box. On one end is a white
incoming power (I'm assuming it's power) lead and a black antenna lead
(with a little black pigtail going to one of the defrost element tabs).
On the other end of this box is a black and red lead. The box itself is
grounded to the body with 2 sheet metal screws.


black (to defrost tab #1)----\ ---defrost tab #2
\ |------------------|
black antenna lead--------------| translucent blue |--------red wire
white lead----------------------| box |
|__________________|--------black wire



The other tab for the defrost element is missing. Am I correct in
assuming the black lead is ground and the red lead goes to the missing
defrost element tab?

Any suggestions would be greatly appreciated.

Cheers,

 

"Chris Mauritz" <ritz@mordor.net> wrote in message
news:Oz2Ib.28789$wz4.5240920@news4.srv.hcvlny.cv.n et...
> OK, after another frosty morning, I decided to tackle my broken rear
> defroster. There's power at the fuse panel and the yellow indicator
> comes on when I press the defrost button. So I popped off the C pillar
> trim and see a strange translucent blue box. On one end is a white
> incoming power (I'm assuming it's power) lead and a black antenna lead
> (with a little black pigtail going to one of the defrost element tabs).
> On the other end of this box is a black and red lead. The box itself is
> grounded to the body with 2 sheet metal screws.
>
>
> black (to defrost tab #1)----\ ---defrost tab #2
> \ |------------------|
> black antenna lead--------------| translucent blue |--------red wire
> white lead----------------------| box |
> |__________________|--------black wire
>
>
>
> The other tab for the defrost element is missing. Am I correct in
> assuming the black lead is ground and the red lead goes to the missing
> defrost element tab?
>
> Any suggestions would be greatly appreciated.
>
> Cheers,
>
>

following my heated wing mirror saga and wire tracking I came to the
conclusion that there must be a relay aft of the cars main wiring, that
controls the rear screen heater element. (1997/98 A4 UK model)

what you describe, could this be a relay (the relay in question)

white input = 12v 10A
red input = 12v signal low power 3/5A (relay coil)
black = radio antenna (top 3 wires of heater element)

as for the red and black wires on output which looks the thicker.....this
should be the heater element at 10/15A rating. The heater fuse in the fuse
box being 10A

one of these is probably ground for the relay coil and the other (thicker)
power to the screen element

only thing is I am not sure why radio antenna would go through this junction

clanger

 

"Clanger" <D231@sidfseltd.freeserve.co.uk> wrote in message
news:bsrk14$l51$1@news5.svr.pol.co.uk...
>
> "Chris Mauritz" <ritz@mordor.net> wrote in message
> news:Oz2Ib.28789$wz4.5240920@news4.srv.hcvlny.cv.n et...
> > OK, after another frosty morning, I decided to tackle my broken rear
> > defroster. There's power at the fuse panel and the yellow indicator
> > comes on when I press the defrost button. So I popped off the C pillar
> > trim and see a strange translucent blue box. On one end is a white
> > incoming power (I'm assuming it's power) lead and a black antenna lead
> > (with a little black pigtail going to one of the defrost element tabs).
> > On the other end of this box is a black and red lead. The box itself is
> > grounded to the body with 2 sheet metal screws.
> >
> >
> > black (to defrost tab #1)----\ ---defrost tab #2
> > \ |------------------|
> > black antenna lead--------------| translucent blue |--------red wire
> > white lead----------------------| box |
> > |__________________|--------black wire
> >
> >
> >
> > The other tab for the defrost element is missing. Am I correct in
> > assuming the black lead is ground and the red lead goes to the missing
> > defrost element tab?
> >
> > Any suggestions would be greatly appreciated.
> >
> > Cheers,
> >
> >
>
> following my heated wing mirror saga and wire tracking I came to the
> conclusion that there must be a relay aft of the cars main wiring, that
> controls the rear screen heater element. (1997/98 A4 UK model)
>
> what you describe, could this be a relay (the relay in question)
>
> white input = 12v 10A
> red input = 12v signal low power 3/5A (relay coil)
> black = radio antenna (top 3 wires of heater element)
>
> as for the red and black wires on output which looks the thicker.....this
> should be the heater element at 10/15A rating. The heater fuse in the fuse
> box being 10A
>
> one of these is probably ground for the relay coil and the other (thicker)
> power to the screen element
>
> only thing is I am not sure why radio antenna would go through this
junction
>
> clanger
>
>

Clanger is right. I haven't checked yet, but there must be some sort of
timer relay for the rear defroster, it might even be built-in, or right
behind the switch.


Romy

 

"Chris Mauritz" <ritz@mordor.net> wrote in message
news:Oz2Ib.28789$wz4.5240920@news4.srv.hcvlny.cv.n et...
> OK, after another frosty morning, I decided to tackle my broken rear
> defroster. There's power at the fuse panel and the yellow indicator
> comes on when I press the defrost button. So I popped off the C pillar
> trim and see a strange translucent blue box. On one end is a white
> incoming power (I'm assuming it's power) lead and a black antenna lead
> (with a little black pigtail going to one of the defrost element tabs).
> On the other end of this box is a black and red lead. The box itself is
> grounded to the body with 2 sheet metal screws.
>
>
> black (to defrost tab #1)----\ ---defrost tab #2
> \ |------------------|
> black antenna lead--------------| translucent blue |--------red wire
> white lead----------------------| box |
> |__________________|--------black wire
>
>
>
> The other tab for the defrost element is missing. Am I correct in
> assuming the black lead is ground and the red lead goes to the missing
> defrost element tab?
>
> Any suggestions would be greatly appreciated.
>
> Cheers,
>
>

I am not clear on the C pillar......do you mean the rear quarter pillar near
back window.

clanger

 

The rear in-window AM antenna is AMPed in C pillar. Not sure but the
defrost might be in the same component but seems unlikely.


Clanger wrote:
> "Chris Mauritz" <ritz@mordor.net> wrote in message
> news:Oz2Ib.28789$wz4.5240920@news4.srv.hcvlny.cv.n et...
>
>>OK, after another frosty morning, I decided to tackle my broken rear
>>defroster. There's power at the fuse panel and the yellow indicator
>>comes on when I press the defrost button. So I popped off the C pillar
>>trim and see a strange translucent blue box. On one end is a white
>>incoming power (I'm assuming it's power) lead and a black antenna lead
>>(with a little black pigtail going to one of the defrost element tabs).
>>On the other end of this box is a black and red lead. The box itself is
>>grounded to the body with 2 sheet metal screws.
>>
>>
>>black (to defrost tab #1)----\ ---defrost tab #2
>> \ |------------------|
>>black antenna lead--------------| translucent blue |--------red wire
>>white lead----------------------| box |
>> |__________________|--------black wire
>>
>>
>>
>>The other tab for the defrost element is missing. Am I correct in
>>assuming the black lead is ground and the red lead goes to the missing
>>defrost element tab?
>>
>>Any suggestions would be greatly appreciated.
>>
>>Cheers,
>>
>>
>
>
> I am not clear on the C pillar......do you mean the rear quarter pillar near
> back window.
>
> clanger
>
>