Rear Screen Heater 80 B3

William Blyth · 30-09-18, 06:08 PM

I've recently replaced the heater matrix on a 1991 Audi 80 b3 1.8 S, and now find that my rear screen heater only works when the dipped lights are on.

The only thing I can think of is that I've found a single cable with no obvious fitting location at the back of the heating controls. Any electricians out there with any ideas?

Mellis46 · 30-09-18, 07:01 PM

Does that cable have a white, funny shaped plug on the end of it? If so its the connection for the 3 auxilliary gauges - it doesnt connect to anything if you haven't got those.

Everything got plugged back in properly behind the dash when you built it back up? Checked all the fuses etc?

William Blyth · 30-09-18, 07:22 PM

The wire was single cable. with a single female connector. I thought I had labelled all the wires as I took them apart, so I was surprised to find an unmarked cable when reconnecting. I was hoping that it may have been an earth cable. Thankyou for your help, at least I can now disregard that cable. That at least leaves me to find another solution to the "rear heater only working with main lights on".

William Blyth · 08-10-18, 10:38 AM

Demister switch now checked and all OK.

Fuse checked - OK.

Checked not connected to Fog Lamps by mistake -OK

Illumination light came on when ignition was turned on

Pressed switch NOTHING

Turned on dipped beam- It works

Davids · 08-10-18, 10:58 AM

No matter how random, tried all the earths, bad earth under a tag and its using the dipper beam as a return path.
Seen it happen before

Just a thought

mikes2 · 08-10-18, 12:35 PM

Disconnect the two fog lamp switches and try it again

30-09-18, 07:01 PM	#2
Mellis46 Aero Advocate Classic Audi Club Member Join Date: Aug 2014 Location: Lancashire Posts: 1,233	Does that cable have a white, funny shaped plug on the end of it? If so its the connection for the 3 auxilliary gauges - it doesnt connect to anything if you haven't got those. Everything got plugged back in properly behind the dash when you built it back up? Checked all the fuses etc? __________________ -1987 90 2.2E / Sapphire Blue (Rest in Pieces) -1989 90 quattro with Sport Equipment / Satin Black -1997 A4 Avant quattro TDI 110 / Tropical Green (Sold) -2012 A1 Sport TFSI / Glacier White (Sold) -2017 A1 Sportback S-line TFSI / Scuba Blue

30-09-18, 07:22 PM	#3
William Blyth Grown up member Classic Audi Club Member Join Date: Jun 2018 Location: Lake District/Borders Posts: 25	The wire was single cable. with a single female connector. I thought I had labelled all the wires as I took them apart, so I was surprised to find an unmarked cable when reconnecting. I was hoping that it may have been an earth cable. Thankyou for your help, at least I can now disregard that cable. That at least leaves me to find another solution to the "rear heater only working with main lights on". Last edited by William Blyth; 01-10-18 at 11:34 AM.

08-10-18, 10:38 AM	#4
William Blyth Grown up member Classic Audi Club Member Join Date: Jun 2018 Location: Lake District/Borders Posts: 25	Demister switch now checked and all OK. Fuse checked - OK. Checked not connected to Fog Lamps by mistake -OK Illumination light came on when ignition was turned on Pressed switch NOTHING Turned on dipped beam- It works Last edited by William Blyth; 08-10-18 at 10:42 AM.

08-10-18, 12:35 PM	#6
mikes2 Senior Member Classic Audi Club Member Join Date: Nov 2007 Location: Polmont Posts: 1,730	Disconnect the two fog lamp switches and try it again __________________ 1991 90 quattro 20v sport 1988 90 quattro project

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08-10-18, 10:58 AM	#5
Davids 4 ring whore! Join Date: Jan 2017 Posts: 2,747	No matter how random, tried all the earths, bad earth under a tag and its using the dipper beam as a return path. Seen it happen before Just a thought