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Discussion Starter · #1 · (Edited)
I have just finished retrofitting automatic headlights and wipers as well as the auto-dimming rear view mirror. I had these options in my last car and it's something I missed. It took a fair amount of research in order to make up all the wires needed, but overall I think it was worth the effort, especially if you can get the parts needed cheaply.

The downside is that a new windscreen is required, and it was this that prompted me when mine became cracked.

Anyway, here are the parts required (trims parts for my coupe with black headlining, roadster and other trim colours may vary).

Parts
Windscreen

8J0 857 511 / E 4PK - Rear view mirror with auto-dimming (black), x1
8E0 971 833 - Flat six pin connector (male) (for mirror), x1
000 979 009 E - Wire set with square pins, x3 (6 pins)

4E0 955 559 C/E or 8K0 955 559 A/D - Rain and light sensor, x1
1C0 973 119 B - Flat three pin connector (male) (for sensor), x1
000 979 009 E - Wire set with square pins, x2 (3 pins)
4F0 907 671 B - Retaining spring for sensor, x1
4E0 955 609 - Sticky pad for sensor (mine was supplied by windscreen company)

4F0 857 593 G 4PK - Cable guide (upper) (black), x1
4F0 857 593 J 4PK - Cable cover (lower) (black), x1

8J2 941 531 L 5PR - Light switch for automatic headlights, front and rear fog lamps, coming/leaving home button, range control and instrument lighting, x1 (varies based on spec/age)
000 979 009 E - Wire set with square pins (extra wire from light switch connector), x1 (1 pin)
8W0 971 636 - Flat six pin connector (male) (for coming home lights button), x1
000 979 009 E - Wire set with square pins, x2 (4 pins)

000 979 009 E - Wire set with square pins (for CECM marked * below), x1 (2 pins)
000 979 150 E - Wire set with clamp pins (for CECM marked ^ below), x1 (1 pin)
000 979 151 E - Wire set with clamp pins (for CECM marked † below), x1 (1 pin)
Piggy back mini blade fuse holder with 5A fuse, x2
Wire - 0.35mm² thin wall, ~17m
Eyelet ground terminal 5.3mm, x1[/ICODE]



Wiring
There is a fair amount of wiring needed, but most go to similar places so it isn't too bad.

Note: early cars, approximately up until 2009, have a CECM. Later cars have a BCM.

Mirror (Y7) connector (6 pins)
Pin 1 > Fuse SC7 in dash fuse box (5A) (positive, ignition live) (already in use (black/yellow), need to splice)
Pin 2 > Earth (negative)
Pin 3 > CECM block B (12-pin connector) T12c, pin 1 ^ or BCM T52c/28 (reverse light signal - to undim) (already in use (black/blue), need to splice)
Pin 4 > (Optional) Split to driver and passenger sides (dimming wing mirror)
Pin 5 > (Optional) Split to driver and passenger sides (dimming wing mirror)
Pin 6 > Interior light, pin 3 * (interior light signal - to undim)

Rain and light sensor (G397) connector (3 pins)
Pin 1 > Fuse SC14 in dash fuse box (5A) (positive, permanent live) (already in use on S-tronic (red/white), need to splice)
Pin 2 > Earth (negative)
Pin 3 > CECM block F (8-pin connector) T8h, pin 3 * or BCM T52b/33 (LIN bus) (already in use (purple), need to splice)

Existing light switch connector (10 pins)
Pin 2 > CECM block E (16-pin connector), pin 14 * or BCM T52a/20 (auto headlight switch)

Coming/leaving home button connector (6 pins) - (CECM only)
Pin 1 > Earth (negative)
Pin 2 > CECM block C (12-pin connector), pin 4 (coming/leaving home button LED) ^
Pin 3 > CECM block E (16-pin connector), pin 12 (coming/leaving home button) *
Pin 4 > CECM block K (10-pin connector), pin 10 (terminal 30g) (already in use, need to splice) †

Dimming mirror wiring.png


Wire lengths
Light switch to CECM - ~70cm
Mirror to CECM - ~190cm
Mirror to earth - ~260cm
Sensor to CECM - ~195cm
Sensor to earth - ~265cm

The wires to the mirror and sensor can be fed from the central electric module (CECM) above the drivers footwell, up the A-pillar and above the headlining. The A-pillar trim just pulls off but it quite stiff (guide here for roadster). The coupe is a bit trickier as the rear trim overlaps it. I found it was best to pull the trim off then remove the rearmost metal clip with needle nose pliers before attempting to twist it out.

Removing the vanity light and central courtesy light makes it easier to feed the wires through and cable tie them to existing wires. I wrapped all my new loom in cloth tape like OEM.

IMG_20170225_171709.jpg


IMG_20170225_171650.jpg


There is an indentation in the centre of the headlining where the wires can be fed through to the rear-view mirror.

To remove the various connectors from the CECM, use the beginning of this guide. I have indicated about which pins were already in use in my car, and this means some will need splicing. I made my own pin removal tool using a bent paperclip and flattened the end with a hammer:

IMG_20170311_130842.jpg


I used piggy back mini blade fuse holders as the fuses were already in use and access is very tight behind the fusebox.

Fitting

The headlight switch is removed by pushing in the knob and rotating clockwise, then pull towards you and it will slide out. The mirror is removed by rotating it, although I'm not sure of the direction as I let the windscreen fitter do the swap. I gave all the new parts to them and they refitted, as they would have to do this anyway.

The rain sensor is attached to the screen with a metal clip before the new screen is fitted:

IMG_20170419_162508.jpg


Coding

Cent. Elect-09 - Long Coding (CECM)
  • Byte 0, bit 5 - enable 'Assistance Driving Light _Leaving Home active'
  • Byte 0, bit 6 - enable 'Rain-/Light sensor installed'
  • Coming/leaving home:
    • Byte 0, bit 7 - enable 'Coming-Home active'
    • Byte 2, bit 4 - enable 'Coming-Home Mode via (0 = 0 Personalisation / 1 = 1 Lightsensor)'
Cent. Elect-09 - Long Coding (BCM)

in progress...
  • Byte 17, bit 4 - 'Assistance Driving Light (ADL) active'
  • Byte 21, bit 5 - 'Rain/Light Sensor (RLS) installed'
  • Byte 24 --- try hex value DC
  • Byte 24, bit 7 -
  • Byte 26, bit 3: 'Daytime Running Light (DRL) only active with Assistance Driving Light (ADL) active'
  • Byte 27, bit 2: 'LED-Daytime Running Light (DRL) Module for Parking/Position Light & Daytime Running Light (DRL)'
  • Coming/leaving home:
    • Byte 12, bit 0 - 'Coming-Home Timer (0 = Start with Term.15 OFF / 1 = Start with Door Opening'
    • Byte 12, bit 2 - 'Coming-Home Mode (0 = automatic / 1 = manual)'
    • Byte 17, bit 3 - 'Coming-Home (CH) via Fog-Lights active'
    • Byte 17, bit 5 - 'Coming-Home (CH) active'
    • Byte 17, bit 6 - 'Leaving-Home (LH) active'

Rain light sensor coding
  • Byte 0, bit 0 - (Optional) enable 'Highway Light Function active (above 140 kph / 90 mph)'
  • Byte 0, bit 1 - enable 'Rain Light Function active'
  • Byte 0, bit 3-4 - '00 Light Activation Threshold normal'
  • Byte 1, bit 0-7 - '49 Light Sensor Correction 73% = Audi TT (8J)'
  • Byte 2, bit 0-7 - '2C Rain Sensor Correction 44% = Audi A5 (8T) / Audi TT (8J)'

Error shown if wired and coded but with sensor removed:

IMG_20170313_192044.jpg


Before the mirror was replaced:

IMG_20170205_152843.jpg


After the mirror was replaced:

IMG_20170419_185509.jpg
 

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Great guide, but as I am not technically minded, glad mine came as standard. Amazing the things you take for granted but miss when they aren't there. Still miss the heated front screen I had on my Focus.

Andy
 

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Had auto lights/wipers on both my TT's, they really work great but not sure I have actually ever seen the auto dimming rear view mirror work. Both my TT's had rear tints, maybe that's the reason? my last TT also had the auto dimming side mirrors, again I never noticed them work at all.

How do you find your auto dimming rear view mirror?
 

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Discussion Starter · #5 ·
I had all three on my old Corsa and although not obvious I did notice the mirror dim at night when I had glare from the wing mirrors. I think if you don't notice it working it is probably just working well, unless the tints do block it. I have tints on my TT but haven't driven it at night yet after fitting.

The auto wipers are definitely a lot better, as you couldn't adjust the sensitivity on my Corsa
 

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Nice write up MT. Must put this on the to do list :) .
 

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Discussion Starter · #7 ·
MT-V6 said:
Mirror (Y7) connector (6 pins)
Pin 1 > Fuse SC7 in dash fuse box (5A) (positive, ignition live) (already in use (black/yellow), need to splice)
Pin 2 > Earth (negative)
Pin 3 > CECM block B (12-pin connector) T12c, pin 1 (reverse light signal - to undim) (already in use (black/blue), need to splice) ^
Pin 4 > (Optional) Split to driver and passenger sides (dimming wing mirror)
Pin 5 > (Optional) Split to driver and passenger sides (dimming wing mirror)
Pin 6 > Interior light, pin 3 * (interior light signal - to undim)

Rain and light sensor (G397) connector (3 pins)
Pin 1 > Fuse SC14 in dash fuse box (5A) (positive, permanent live) (already in use on S-tronic (red/white), need to splice)
Pin 2 > Earth (negative)
Pin 3 > CECM block F (8-pin connector) T8h, pin 3 (LIN bus) (already in use (purple), need to splice) *

Existing light switch connector (10 pins)
Pin 2 > CECM block E (16-pin connector), pin 14 (auto headlight switch) *

Coming/leaving home button connector (6 pins)
Pin 1 > Earth (negative)
Pin 2 > CECM block C (12-pin connector), pin 4 (coming/leaving home button LED) ^
Pin 3 > CECM block E (16-pin connector), pin 12 (coming/leaving home button) *
Pin 4 > CECM block K (10-pin connector), pin 10 (terminal 30g) (already in use, need to splice) †
Recently I have been asked about the differences between prefacelift and facelift in what is required to complete this mod. I have not done this myself, but this is what I believe to be correct based upon studying the parts catalogue and wiring diagrams.

Mirror (Y7) connector (6 pins)
Pin 1 > Same as prefacelift
Pin 2 > Same as prefacelift
Pin 3 > T52c/28, will need to splice
Pin 4 > Same as prefacelift
Pin 5 > Same as prefacelift
Pin 6 > Same as prefacelift

Rain and light sensor (G397) connector (3 pins)
Pin 1 > Fuse SC14 up to May 2009 / SC15 from June 2009
Pin 2 > Same as prefacelift
Pin 3 > T52b/33, will need to splice

Existing light switch connector (10 pins)
Pin 2 > T52a/20

Coming/leaving home button connector (6 pins)
I don't believe there is a part available for this even though there are some references in the wiring. Can be set in the DIS

Aside from the headlight switch, the parts are the same. The headlight switch differs based on RHD/LHD, front foglights/xenon headlights and DRL etc, there are many variations.
 

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Thanks very much for looking this up for me. Just for anyone else looking at this guide for a facelift TT I have added the below diagram from the service manual which should help with the pin locations provided above and have marked the pins with coloured dots.

Screenshot 2021-02-11 185228.jpg


1 - 52-pin connector -T52a- , black on wiring harness
2 - 52-pin connector -T52b- , yellow on wiring harness
3 - 52-pin connector -T52c- , brown on wiring harness

Also my parts list as follows:
Rear view mirror - 8J0 857 511 4PK
Rain/light sensor - 8K0 955 559 D (Replaces 4E0 955 599 E but still try this for cheaper used options)
Light switch - 8J2 941 531 AA
Retainer spring - 4F0 907 671 B
Gel pad - 4E0 955 609

MT-V6 - Regarding the rain sensor, I have noticed there are many on eBay with the part number 8K0 955 599 only (no letter after the code). Any idea if this part is the same as the part numbers I have listed above?

Also, how have you spliced into the existing fuses and wiring? Any chance you could help me with this please? I assume with the other pins you just push them into the existing connectors?
 

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Discussion Starter · #9 ·
Nipun said:
MT-V6 - Regarding the rain sensor, I have noticed there are many on eBay with the part number 8K0 955 599 only (no letter after the code). Any idea if this part is the same as the part numbers I have listed above?

Also, how have you spliced into the existing fuses and wiring? Any chance you could help me with this please? I assume with the other pins you just push them into the existing connectors?
That sensor doesn't show as compatible with the TT, is listed for the A1, A4, A5, A8 and Q5

These should all be compatible: 4E0 955 559 C, 4E0 955 559 E, 8K0 955 559 A, 8K0 955 559 D

I took the pin out of the existing connector, cut a small amount of insulation of, twisted on the new wire, soldered, slid a piece of heatshrink over and then put the pin back into the connector. Yes, the other ones can go straight into the empty slot

Also, you are in luck as I just cross referenced the prefacelift and the facelift pins, and they are the same type, so the Kufatec loom should be easy to fit :)
 

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Thanks for confirming regards the sensor and regards the splicing. I like your method, that way the existing wiring isn't necessarily cut into.

Just ordered the loom from Kufatec too. I did price up making the loom, but at £35 delivered the Kufatec one is decent value, especially since the pins are the same, thanks again for looking this up :D

I had a look at the connectors behind my existing light switch, it seems pin 2 is already in use (as I have the DRL switch currently). Do you think I'll just be able to follow this wire to the control module and move it to t52a-20?
 

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Discussion Starter · #11 ·
Are you sure the existing wire was pin 2 of the 10 pin connector?
 

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Discussion Starter · #13 ·
Ah yes that does make sense, I forgot that the facelift TTs come with a 4 position switch with the DRL position (pre facelifts have the DRL on a separate switch)

I'll double check the wiring diagram as there is probably a note I missed

Would also be interested to confirm if the wire does go to the right place already. If so, that's a bit less for you to do :)
 

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MT-V6 said:
Ah yes that does make sense, I forgot that the facelift TTs come with a 4 position switch with the DRL position (pre facelifts have the DRL on a separate switch)

I'll double check the wiring diagram as there is probably a note I missed

Would also be interested to confirm if the wire does go to the right place already. If so, that's a bit less for you to do :)
Just to pick up on this, I had a root around today investigating the connections. I can confirm that PIN 2 from the light switch does indeed go to T52A - PIN 20 already. Tested with a multi meter to be sure. So a little less wiring for me which is nice :p

20210228_164311.jpg
T52A PIN 20

20210228_165207.jpg
T52B PIN 33

20210228_205012.jpg
T52C PIN 28

I should add the diagram I posted above from the workshop manual marking the pins seems to be reversed, which was throwing me off massively at first! Not sure why? Maybe a LHD RHD thing...
 

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Discussion Starter · #15 ·
Nipun said:
I should add the diagram I posted above from the workshop manual marking the pins seems to be reversed, which was throwing me off massively at first! Not sure why? Maybe a LHD RHD thing...
Note the diagram is of the module itself, so you are viewing the connectors from 'the rear'. That is why it is reversed :)
 

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MT-V6 said:
Nipun said:
I should add the diagram I posted above from the workshop manual marking the pins seems to be reversed, which was throwing me off massively at first! Not sure why? Maybe a LHD RHD thing...
Note the diagram is of the module itself, so you are viewing the connectors from 'the rear'. That is why it is reversed :)
Haha of course :roll: (face palm!)
 

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MT-V6 said:
I have just finished retrofitting automatic headlights and wipers as well as the auto-dimming rear view mirror to my 2007 TT. I had these options in my last car and it's something I missed. It took a fair amount of research in order to make up all the wires needed, but overall I think it was worth the effort, especially if you can get the parts needed cheaply.

The downside is that a new windscreen is required, and it was this that prompted me when mine became cracked.

Anyway, here are the parts required (trims parts for my coupe with black headlining, roadster and other trim colours may vary):

Code:
                    | Windscreen

8J0 857 511 4PK     | Rear view mirror with auto-dimming (black), x1
8E0 971 833         | Flat six pin connector (male) (for mirror), x1
000 979 009 E       | Wire set with square pins, x3 (6 pins)

4E0 955 559 E       | Rain and light sensor, x1
1C0 973 119 B       | Flat three pin connector (male) (for sensor), x1
000 979 009 E       | Wire set with square pins, x2 (3 pins)
4F0 907 671 B       | Retaining spring for sensor, x1
4E0 955 609         | Sticky pad for sensor (mine was supplied by windscreen company)

4F0 857 593 G 4PK   | Cable guide (upper) (black), x1
4F0 857 593 J 4PK   | Cable cover (lower) (black), x1

8J2 941 531 L 5PR   | Light switch for automatic headlights, front and rear fog lamps, coming/leaving home button, range control and instrument lighting, x1
000 979 009 E       | Wire set with square pins (extra wire from light switch connector), x1 (1 pin)
8W0 971 636         | Flat six pin connector (male) (for coming home lights button), x1
000 979 009 E       | Wire set with square pins, x2 (4 pins)

000 979 009 E       | Wire set with square pins (for CECM marked * below), x1 (2 pins)
000 979 150 E       | Wire set with clamp pins (for CECM marked ^ below), x1 (1 pin)
000 979 151 E       | Wire set with clamp pins (for CECM marked † below), x1 (1 pin)
                    | Piggy back mini blade fuse holder with 5A fuse, x2
                    | Wire - 0.35mm² thin wall, ~17m
                    | Eyelet ground terminal 5.3mm, x1
Wiring
There is a fair amount of wiring needed, but most go to similar places so it isn't too bad.

Mirror (Y7) connector (6 pins)
Pin 1 > Fuse SC7 in dash fuse box (5A) (positive, ignition live) (already in use (black/yellow), need to splice)
Pin 2 > Earth (negative)
Pin 3 > CECM block B (12-pin connector) T12c, pin 1 (reverse light signal - to undim) (already in use (black/blue), need to splice) ^
Pin 4 > (Optional) Split to driver and passenger sides (dimming wing mirror)
Pin 5 > (Optional) Split to driver and passenger sides (dimming wing mirror)
Pin 6 > Interior light, pin 3 * (interior light signal - to undim)

Rain and light sensor (G397) connector (3 pins)
Pin 1 > Fuse SC14 in dash fuse box (5A) (positive, permanent live) (already in use on S-tronic (red/white), need to splice)
Pin 2 > Earth (negative)
Pin 3 > CECM block F (8-pin connector) T8h, pin 3 (LIN bus) (already in use (purple), need to splice) *

Existing light switch connector (10 pins)
Pin 2 > CECM block E (16-pin connector), pin 14 (auto headlight switch) *

Coming/leaving home button connector (6 pins)
Pin 1 > Earth (negative)
Pin 2 > CECM block C (12-pin connector), pin 4 (coming/leaving home button LED) ^
Pin 3 > CECM block E (16-pin connector), pin 12 (coming/leaving home button) *
Pin 4 > CECM block K (10-pin connector), pin 10 (terminal 30g) (already in use, need to splice) †

View attachment 7

Wire lengths
Light switch to CECM - ~70cm
Mirror to CECM - ~190cm
Mirror to earth - ~260cm
Sensor to CECM - ~195cm
Sensor to earth - ~265cm

The wires to the mirror and sensor can be fed from the central electric module (CECM) above the drivers footwell, up the A-pillar and above the headlining. The A-pillar trim just pulls off but it quite stiff (guide here for roadster). The coupe is a bit trickier as the rear trim overlaps it. I found it was best to pull the trim off then remove the rearmost metal clip with needle nose pliers before attempting to twist it out.

Removing the vanity light and central courtesy light makes it easier to feed the wires through and cable tie them to existing wires. I wrapped all my new loom in cloth tape like OEM.



View attachment 1

There is an indentation in the centre of the headlining where the wires can be fed through to the rear-view mirror.

To remove the various connectors from the CECM, use the beginning of this guide. I have indicated about which pins were already in use in my car, and this means some will need splicing. I made my own pin removal tool using a bent paperclip and flattened the end with a hammer:

View attachment 6

I used piggy back mini blade fuse holders as the fuses were already in use and access is very tight behind the fusebox.

Fitting

The headlight switch is removed by pushing in the knob and rotating clockwise, then pull towards you and it will slide out. The mirror is removed by rotating it, although I'm not sure of the direction as I let the windscreen fitter do the swap. I gave all the new parts to them and they refitted, as they would have to do this anyway.

The rain sensor is attached to the screen with a metal clip before the new screen is fitted:

View attachment 2

Coding

Cent. Elect-09 - Long Coding
  • Byte 0, bit 5 - enable 'Assistance Driving Light _Leaving Home active'[/*]
  • Byte 0, bit 6 - enable 'Rain-/Light sensor installed'[/*]
  • Byte 0, bit 7 - enable 'Coming-Home active'[/*]
  • Byte 2, bit 4 - enable 'Coming-Home Mode via (0 = 0 Personalisation / 1 = 1 Lightsensor)'[/*]

Rain light sensor coding
  • Byte 0, bit 0 - (Optional) enable 'Highway Light Function active (above 140 kph / 90 mph)'[/*]
  • Byte 0, bit 1 - enable 'Rain Light Function active'[/*]
  • Byte 0, bit 3-4 - '00 Light Activation Threshold normal'[/*]
  • Byte 1, bit 0-7 - '49 Light Sensor Correction 73% = Audi TT (8J)'[/*]
  • Byte 2, bit 0-7 - '2C Rain Sensor Correction 44% = Audi A5 (8T) / Audi TT (8J)'[/*]

Error shown if wired and coded but with sensor removed:

View attachment 3

Before the mirror was replaced:

View attachment 4

After the mirror was replaced:

View attachment 5
I'm looking to do the same on my MK2 TT roadster, how did you get the coding done?
 

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Discussion Starter · #18 ·
With VCDS
 

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lozzzzzer said:
I'm looking to do the same on my MK2 TT roadster, how did you get the coding done?
It's funny that you've resurrected this thread as today I've been trying to get my cracked windscreen replaced with the correct one needed to house the rain sensor and dimming mirror but my insurance company (Hastings) won't authorise it. They will only replace the screen "like for like". Just something to note if your planning to go down the insurance route for your windscreen.

MT - did you go through insurance for yours or did you replace privately?
 

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Discussion Starter · #20 ·
At the time I found that Autoglass's system was clever enough to know my car had 'non-sensor' glass and they couldn't be convinced otherwise over the phone. National Windscreens system did not know, and I just told them it had the sensor. The fitted was confused at first but when I explained I was fitting it they were happy. I had the wires in place and the new mirror, and he even fitted that all in place with the trim clips etc
 
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