Audi A3 8Y seats into a Mk7.5 R

[GeoffT]

My Mk7.5 R has the factory leather seats. They do look good but this summer has confirmed all I ever thought about leather for car seats being a really bad idea. If the heat generated by solar energy through glass onto leather surfaces could somehow be harnessed for the good of mankind rather than just burning the occupants legs and backs, the world would be a better place, but as far as I know it can't. 

 

So inspired by this thread:

and the knowledge that Mk8 seats are plug and play I started looking at the options.

 

Either it is an "Emperor's new clothes" situation or I am on my own with this opinion (wouldn't be the first time) but I don't like Alcantara. I genuinely don't understand how a material that looks scruffy and patchy even before anyone has sat on it, has become so universally popular for car seating. 

 

I started by looking at the various Golf Mk8 seat versions. Although I like the shape of them, all of the different variations (R/R Line/GTD/GTI/ClubSport/GTE) have Alcantara somewhere and I'm not a fan of the jazzy / tartan fabric on a lot of them.  I have always preferred subtle and understated to jazzy and in your face.  

 

So I spent hours trawling through Ebay looking at all VAG seats I could find for one that fitted my criteria and that I liked the look of. 

 

I could probably now go on Mastermind with specialist subject "VAG MQB platform car seats  2018 to present day".   

 

Anyway, I finally made a decision and have just bought a pair of Audi A3 8Y 2025 Sport seats. I think they were a real bargain. While the Golf Mk8 seats were typically asking £1100 or more a pair, these were just under £300 the pair including delivery and come from a car that has only done 1,100 miles. In the pictures they look mint as you'd expect with that little use.

 

This is a library picture of those seats in an A3. As well as the normal front/back, up/down, back tilt adjustments, they also have electric 2 way adjustable lumbar, separate base tilt and adjustable thigh support. All the material is proper fabric! I'd have preferred them without the stripe across the top, but I could find nothing that was 100% perfect and these seemed my best option. I have done a lot of research into the wiring situation and am pretty confident that with Stan the Man's help I can get them  working. To be continued...........!

[SpursMadDave]

Stan will sort the wiring out no problem, he got some 2010 S3 Wingbacks working with heating no problem in my MK7

[GeoffT]

The seats are now here and I'm very pleased with them. After a bit of a vac they look like new and the stripe that I wasn't over keen on from the pics, looks much better in the flesh.

 

 

[GeoffT]

So the wiring! 

 

After a lot of googling/testing and checking cable runs I am fairly confident I have all the cables identified.

 

The connectors fitted are:

 

Drivers Side

17 pin red connector - power etc

6 pin green connector - seat heating

5 pin flat black connector - seat belt buckle & seat occupancy switch

3 pin yellow - airbag (2 off - the drivers seat has an additional airbag in the centre which has a slightly different connector)

 

Passenger Side

17 pin red connector - power etc

6 pin green connector - seat heating

5 pin flat black connector - seat belt buckle & seat occupancy switch

3 pin yellow - airbag

 

The main "doorside" airbag connectors are the same as my Golf. I didn't even know a second drivers airbag in the centre was a thing until I saw a pic on Ebay of a seat where one had deployed. Obviously the mk7.5 would have no way of firing that one so I will just be leaving that one disconnected.

 

Pinouts (all seem to be the same on both sides - even the drivers side has a seat occupancy switch fitted)

 

17 pin red connector pinout 

 

Pin 9: Thin White Positive to under seat LED (I won't be using this so haven't investigated if this is full 12v/dimmable etc)
Pin 11: Thin Brown Earth for under seat LED
Pin 15 :Thick Red 12V supply for Lumbar Control Power
Pin 16: Thick Brown wire – Main seat frame ground
 

6 pin green connector 

 

Pin 1: Thin Green/Brown Heating Thermistors Ground
Pin 2: Thin White  Heating Thermistor Base Signal  (5k ohm as gets hotter 8k ish ohm at room temp)
Pin 3: Thick Brown Ground for both heater elements
Pin 4: Thick Red/White Base Heater element (3.0 ohm to brown)
Pin 5: Thin Blue  Heating Thermistor Back Signal  (5k ohm as gets hotter 8k ish ohm at room temp)
Pin 6: Thick Green Seat Back heater element (3.0 ohm to brown)

 

5 pin flat black connector

 

Pin 1: Thin Brown Ground for Seat Occupancy and Seatbelt Buckle
Pin 2: Thin Green Seat belt Buckle switch (closed to ground when unbuckled, open when buckled)
Pin 3: Thin Blue/Green Seat Occupancy Signal (430ohm unoccupied 130ohm occupied)
Pin 4: Thin Red (goes to part 8Y0 980 341 on seat rail – seat position sensor) 
 

With regard to the Seat heating, Audi have now spilt the base and back elements and sensors into 2 completely distinct circuits. They share a common ground but there are 2 heating element supply pins and 2 thermistor output pins. I don't know how that is controlled in the OEM Audi system, but it looks like they could have completely different settings for base and back, but obviously you would need the Audi control system to achieve that . 

 

The resistance values of each heating element and sensor are exactly the same as my Mk7.5 so I will be just connecting the back circuit/sensor cables to the car. As they are cloth seats heating is not really necessary at all but as the car has the buttons and control circuitry I might as well have a back-warming facility for our poor ageing backs if needed!

 

 

 

 

 

 

[GeoffT]

Pictures of connectors 

[GeoffT]

Slight delay to the install after I found a strange anomaly with the seatbelt buckle switches when I was treble checking the wiring. 

 

On the passenger side when unbuckled the resistance across the 2 pins is virtually 0 ohm and when buckled it goes open circuit (ie it is basically just a microswitch)

 

But on the driver side when unbuckled the resistance across the 2 pins is 400 ohm and when buckled it is 100 ohm. I have absolutely no idea why this would be, but I measured it many times with the same result. 

 

So I checked the buckle switch resistance in my 7.5 and found that in that both sides are the same at nearly 0 ohm unbuckled, open circuit buckled - so again both sides are just a switch and the same as the Audi passenger side buckle. 

 

I did think about just moving the buckles from my 7.5 over to the Audi seats, but the mounting method is very slightly different between the 2 and I don't want to take any chances with safety items.   

 

Fortunately it turns out that the Audi buckles are physically identical for both sides, so you can just flip them over and bolt them to the other side - the only difference is the resistance within the switch part. So I have ordered another passenger side seat belt buckle from Ebay. Presuming the resistance is the same as my existing passenger side one when it arrives I will fit that to the drivers side and I should be good to go.

 

I'm presuming that as people have successfully swapped Mk8 Golf seats into a Mk7.5 with no seatbelt warning issues, VW didn't go down the same weird drivers/passengers side different resistance route that Audi chose.

 

 

 

 

[GeoffT]

Well the seat belt buckle issue took way longer to sort than it should.

 

To work with Golf MK7.5 wiring, you need both seat belt buckles to be part code 8Y0857755 and NOT 8Y0857755A. The “A” version is the one with the 400 ohm/100 ohm switch rather than the simple on/off one. Audi fit that to the drivers side.

 

But as the codes are only one letter different and look physically identical, I have already had 2 of the wrong item send from Ebay, despite being listed as passenger side versions 

 

The second one I ordered I double checked their listing photos which definitely showed the part number I wanted, but they still sent me a different one to the one in the pics and it was another driver's side“A” version.

 

Looking into it a bit further, most VAG platforms of the same age as the Golf Mk8/Audi 8Y use the 8Y0857755 buckles on both drivers and passenger sides, it only seems to be Audi that complicates it.

 

So, if anyone does go down the track of fitting Audi A3/S3 8Y seats in a Golf 7.5, I would advise getting the extra seat belt buckle you need from a VW Golf8/Polo/ID.3/ID.4 or Seat Leon etc etc as it then doesn’t matter which side you get. I also found that the same part number listed for a Seat Leon was 25% cheaper than ones listed for Audi !

 

Anyway finally it was 3rd time lucky and (for £15) I now have a 8Y0857755 seat belt buckle from a Seat Leon fitted to my Audi drivers seat and which will (or at least should) now work with my Mk7.5 electronics.

 

Having completed my wiring harness while I was waiting for the correct seat belt buckle to arrive, I am finally ready to do the install which I hope to complete this week sometime.
 

[GeoffT]

After a couple of false starts, the seats are now in and everything is working great. 👍

No airbag warnings. I wasn’t expecting any as they were plug and play with the Mk7.5 connectors, but still a relief to reconnect the battery with no airbags going off or warnings popping up!

Passenger seat occupancy detector working correctly. I think for US spec cars that is a bit more complicated as they seem to have a separate module under the seat controlling the occupancy/airbag logic, but for UK cars it is just a basic switch.

Seat belt buckle switches working both sides.

Electric Lumbar adjustment working fine. I ran cables for this into the centre console where I already had a connector block tapped into the 12V socket feed.

Seat Heating. As I described earlier Audi have split this into separate base and back circuits both of which have the same characteristics as the Mk7.5 full seat heating. So I just connected the back circuits and it is working fine if I ever need it.

 

Total cost of the project was around £320 by the time I’d added the cost of another seat belt buckle for the drivers side and the connectors for the wiring. I got the connectors from here:
6 pin connectors (Audi Heating Connector) https://www.aliexpress.com/item/1005009657381710.html
17 pin connectors. (General VW connector and Audi Power connector) https://www.aliexpress.com/item/1005006296307219.html

 

I love the look of them and having adjusted them just as I want, they seem very comfortable and supportive. 

 

And as I will now no longer get burned legs at the end of a long, hot, sunny day, I think I can also take credit for the end of the heatwave!