GeoffT

I know I am like a dog with a bone over this, but I do feel very strongly about AI giving out wrong information. So I have just been arguing with AI regarding the original statement that there are fundamental differences between Mk7.5 and Mk8 seat heating mats and sensors. Finally it agrees with me! My question when AI stated there was a fundamental difference between Mk7.5 and Mk8 seat heating: "That again is incorrect. The resistance curve is identical between Mk7.5 and Mk8 seats. Where did you get the information that it is different from?" AI response: (my bold) You are completely right, and I sincerely apologise. The initial information provided was incorrect—the underlying component hardware, the NTC thermistors, and their resistance curves are indeed identical between the Golf Mk7.5 and Mk8.The misconception about a differing resistance profile stem from early automotive forum threads and documentation where DIYers ran into errors during seat swaps. The root cause of those errors was misinterpreted:The Actual Cause: The error codes and system shutdowns during retrofits are entirely caused by differences in control modules and electrical architecture, not the thermistor hardware.Architecture Change: On the Mk7.5, the seat heating circuits route back and communicate directly with the Central Electrics module (J519). On the Mk8, Volkswagen transitioned the control loop directly to the Heater and Air Conditioning system module (J979).Because the thermistor and the heating mats themselves share the exact same operational resistance profile, they can be successfully pinned out and run if the correct module logic is satisfied.Thank you for correcting that. Are you currently pinning out a harness for a swap, or testing a specific sensor?

Sorry, but that shows AI has no idea how the system actually works.As I explained above, the 3 way heating control is entirely controlled from the car end, not the seats themselves. There is no logical way that it could only work as on/off. If it works at all it will work as OEM with 3 settings. Although my Audi seats have 2 seperate circuits for base and back (unlike the Mk8 seats which have just one) with the back circuit connected to my 7.5, the full 3 stage OEM heating works perfectly (EDIT see pics attached). I am convinced from all of the official diagrams I have seen that the Mk8 seats when wired correctly would give full OEM 3 stage heating.

Just FYI another forum I use for Hubitat Home Automation has just introduced this: https://community.hubitat.com/t/new-community-guideline-for-ai-generated-content/165886

All fair points.

I think that would be the perfect solution 👍

https://www.vwvortex.com/threads/swapping-mk8-gti-seats-to-mk7-5-sportwagen.9561713/?utm_source=google&utm_medium=organic This guy says the seat heating works for a Mk8 GTI Seat in his Mk7.5. I guess there aren't too many people that have fitted Mk8 seats into a Mk7.5 anyway and all the ones I am aware of in this country have all fitted cloth seats where seat heating is a very low priority. Also, anyone reading your post in the Mk8 Seat thread on here will probably have taken it as gospel that it wouldn't work and not even tried. It's only stubborn old buggers like me that question it! BTW the 3 stage heating is nothing special and doesn't require anything specific within the seats themselves. There is no CANBUS command between car and seat for any of this. All the car does is apply different temperature parameters for each of the 3 settings (which I think can be adjusted with VAGCOM etc) and just varies the PWM of the 12V supply to increase or decrease the effective power. Within the seat itself is just a heating mat circuit and a thermister circuit to measure temperature. I had my seat heating working on my Study floor with just a simple 12V power supply.

Sorry Rebecca, I thought the link I posted linked directly to the relevant post but it didn't. It was this post by @delboy1 on page 4 of the thread. I asked him later in the thread where that info came and was it from VW and he said no, it was from AI. Again I want to stress I'm not having a pop at the poster, just concerned at the unintended consequences of it. From my testing and looking at official wiring diagrams, none of the information in the post is accurate, so I have no idea where AI got it from in the first place.

I'm not sure if there is already a forum policy on this, but if there isn't maybe there should be? I think any information that is taken from AI should clearly be labelled as such in a post as a caveat that is may well be wrong. Not having a personal dig at anyone as this is all relatively new ground anyway and the info was posted in good faith, but there is a post here that was not posted as being sourced from AI, but the OP later said it was. The information in it turned out to be completely incorrect. But because it was now on a forum, it gets found by the AI bots to reinforce it's own wrong information. While fitting some Audi seats into my Mk7.5, I have been doing a lot of searches on Google generally, and have found that at least 90% of what the AI part of the search returns is incorrect. I have even challenged it a couple of time and it has apologised, and then (sometimes) actually come up with the correct info. But if I do the exact same search again, it still comes up with the original incorrect info, despite admitting it was incorrect previously.

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!

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.

Mine has done 55,000 but I'm 66 so mine has less years to last! 🤣

It was my mate's turn to drive for a golfing day out this week and by the time we got back to our home course car park where my car was parked, it was pretty nearly deserted. So we drove up towards my car with a clear view of it from the side and then 3/4 rear. It reminded me just what a great looking car the 7.5 R is. Normally I only get to see it close up or parked between other cars (mostly huge, ugly SUVs), but looking at it again like that I reckon it's a design classic. With the way it drives as well, it's definitely a keeper!

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.

I reckon that somewhere in the seat heating menu settings for the 8Y, it must let you adjust the balance of heat between base and back. I don't see the point in having distinct curcuits otherwise. I plan to just connect the back heating circuit to my car. As they are cloth seats there isn't really any need for any heating anyway, but the option for a bit of heat on our old backs will be a nice to have feature. I really only did all this testing to try to debunk the theory that Mk8 seat heating couldn't work in a Mk7.5. Because the 8Y seat is wired differently to the Mk8, I havent 100% done that, but I'm pretty sure now that as the Mk8 is only a single hesting circuit it should just be a case of connecting the element and sensor to the right pins on a Mk7.5 and it will work.

Yes, I think so! "Stan the Man" who is the VAG wiring adaptor Guru seems to still be away (or has run for the hills having looked at what I'm attempting!) but I have ordered some connector parts anyway to make up a conversion loom myself if necessary.