Flip the seat upside down and you will notice I think they are called HOG RINGS. Well you can use a pair of pliers to undo the ring there are 2 - 3 on each side left nright at the back of the seat.

Now you have to remove these other 2 T-15 bolts attached to these plastic covering. This will give you access to pull off the bottom seat baffle. It is held on by a long plastic molding/clip and can be easily popped up with either your fingers or a flathead screwdriver. Just work your way pulling up that molding and you will eventally hve the bottom part of your seat free. (Note: On the passenger side bottom protin of the seat, there is a sensor that has to do with the airbag. It is part of the seat and shld be dealt with delicately.)

Step 4: Take your non-heated seat baffles to an upholstry shop and have them put the heated elements into them. In the meantime let's work on your wiring harness considering you wo't be able to drive with no seats. haha

Step 5: I opted not to puchase the OEM BMW retofit kit simple because I wanted a challenge first off, and second I wasn't going to pay ~ $300 for a wiring harness and button panel that I could easily make and obtain. First lets look at Heated Seat Retrofit PDF manual, it gives detailed information on the wirig harness. I read through i and simplified what the harness is all about here is the way I saw it as:

To Passenger seat Side:

• B1 - Seat Heating On (GN/YE) - Plug X279 Pin 25
• B2 - Ground (BR) - Plug X279 Pin 24
• B3 - Temperature (WT/BL) - Plug X279 Pin 23
• B4 - Ground (BR) - Under Pass Side Skirt (B2 <---> B4)

To Driver seat Side:

• A1 - Seat Heating On (GN/VI) - Plug X275 Pin 25
• A2 - Ground (BR) - Plug X275 Pin 24
• A3 - Temperature (WT/GN) - Plug X275 Pin 23
• A4 - Ground (BR) - Under Driver Side Skirt (A2 <---> A4)

To Console Switch:

Passenger Side:

• B1.1 - Seat Heating On (GN/YE) - X1869 Pin 1 (B1 <---> B1.1)
• B3.1 - Temperature (WT/BL) - X1869 Pin 20 (B3 <---> B3.1)

Driver Side:

• A1.1 - Seat Heating On (GN/VI) - X1869 Pin 13 (A1 <---> A1.1)
• A3.1 - Temperature (WT/GN) - X1869 Pin 21 (A3 <---> A3.1)

To Fuse Panel:

• C - K-bus (WT/RD/YE) Fuse Box Joint Connector X10116 (Trigger/Accessory Wire) Pin 23 - Console Switch
• D - Terminal 30 (RD/VI) Fuse Holder A46 slot No. F42 (30 amp) Pin 7 - Console Switch
• E - Terminal R (VI/BL) Fuse Holder A47 slot No. F12 (7.5 amp) Pin 22 - on Console Switch

As you can see I simpilfied it or at least to me it seems that way. Anyways lets start wiring.

Step 6: Removing Glove Box and Driver side steering column panel, both are held in by philips head screws. Now lets start making your wiring harness. Starting with the drivers side you need 3 wires (1 for Ground, 1 for Temperature, and 1 for Power (Heating On function) I didnt have the multicolored wires like BMW so I just made do with what I had. I tried to match the wire colors up as best I could for instance if the OEM wire was White/Green I would make my wire White etc..

Drivers Side:

16 Gauge wire: (The Green Wire should have been 14 Guage but I didn't have any available and the 16 Gauge should be fine)

White - 9 ft (Temperature Wire) - Pin 23 at the Drivers Seat Plug
Green - 9 ft (Heating On Wire) - Pin 25 at the Drivers Seat Plug


Brown - 3 ft (Ground Wire) - Pin 24 at the Drivers Seat Plug

 

I routed the wires under the foot trims and behind the steering column panel to the consle area where the accessory panel with the heated seat buttons will be located. The Ground wire is connected in a Stock Grounding point underneath the carpet. You need to pull the carpet up a little bit in order to access it and there are a few empty slots (Note: You will need a OEM pin connector to get it to secure correctly you will need to crimp or solder this connector to the Brown wire in order to supply a Ground connection to the seat)

Passengers side is the same method as the drivers side in terms of routing the wires. The Grounding point will be bend the carpet, and youwill rute the wires behind the fuse panel to the console area where the heated seat buttons are located. The wire colors I used for the Passenger side are:

Blue - 9 ft (Temperature Wire) - Pin 23 at the Passengers Seat Plug
Yellow - 9 ft (Heating On Wire) - Pin 25 at the Passengers Seat Plug
Brown - 3 ft (Ground Wire) - Pin 24 at the Passengers Seat Plug

Fuse Panel:

The fuse panel is suspended by 2 plastic knobs, you must open the fuse panel and then push the fuse panel up in order to release the panel from it's mounting points. Once this is accomplished the fuse panel will drop down and give you more room to access and play around with.

Now running wires into the fuse panel is a little tricky yet still doable. You will need an additional 3 wires plus some OEM BMW connectors:

1 - 12 Gauge Wire ~ 7 ft - Red (Run this wire from fuse #42 - 30 AMP Fuse to the center console area, this s what supplies most of your power to your heated seats
2 - 16 Gauge Wires ~ 7 ft each
- Red/Yellow (Run this wire from the comb connector that has all the Red/White/Yellow Wires on the fuse panel to the center console area. This is basically turn on LEd for the Heated Seats)

 

- Blue (Run this wire from fuse #12 - 7.5 AMP Fuse to the center console area)
Step 7:

Now working at the center console area with the 23 pin plug connector. You just ran 7 wires to the console area. Those being:

1. White
2. Green
3. Blue
4. Yellow
5. Red
6. Red/Yellow
7. Blue

These connect to the 23 pin plug at the center console area in the following order. You must crimp or solder the connections and put them into the 23 pin plug connector.

1. White - Pin 21
2. Green - Pin 13
3. Blue - Pin 20
4. Yellow - Pin 1
5. Red - Pin 7
6. Red/Yellow - Pin 23
7. Blue - Pin 22

Note: There is also a little 3 pin connector on the backside of the accessory panel you can plug n your DSC (4 pin) connector to this the new panel uses one less wire which I think is 12v Constant because it is now being supplied from the fuse panel.

Step 8:

Now go back to other the Drivers and Passengers side harness that are found underneath the seats. You must unlock the connectors first. Once you have done this now locate on the:

Drivers Side: Pins 23-25 Crimp or solder the pinout connectors as follows:

Pin 23 - White
Pin 24 - Brown
Pin 25 - Green

 

Passenger Side: Pins 23-25 Crimp or solder the pinout connectors as follows:

Pin 23 - Blue
Pin 24 - Brown
Pin 25 - Yellow

Now lastly resecure the connectors and you are done with the wiring portion.

Step 9:

Pick up your seats from the Upholstry shop if you don't have them already and begin to reassemble your seats. Installation is the reverse of removal only difference is that you must swap out the seat belts that come with the additional wiring for heated and power seats. Using your T-45 socket undo the seatbealt and trace the wiring undoing the plastic clips that secure the wiring harness and remove the old connector. Installation of the new seatbelt and wirng harness is the reverse of the process youjust used to remove the old one. Also there is a 2-3 pin male and female connector that connect both the backrest of the seat and the bottom part of the seat make sure it is connected or else the heating elements will not work.

 

Step 10:

Once the seats are reassembled, put them back into your car and bolt them down torquing everything to spec. Plug in the 25 pin female plug connector under the seats to the new male wiring harness attached to the seats.

Now working at the center console area plug in the 23 pin plug connector to the back of the accessory panel and the also the 4 pin plug connector if applicable.

Step 11:

Reconnect your battery, and start your car. And.... there you have it, heated seats!!! Push the button once and all 3 lights on the button should light up. Push it a second time and only 2 will light up, this is part of the temperature setting to set at a certain temperature.

Once Everything is working correctly reinstall everything (Foot Sills, Covers, GolveBox everything is reverse of removal) Just a quick note: the wire colors I used are for my reference only because those are the colors I chose to use they are not the BMW OEM Wire colors as found in the retrofit PDF file. Also if anyone wants the retrofit pdf file just PM me with your email and I will gladly send it to you, unless someone would be kind enough to host it for me and everyone on the forum.

Well I have to say this retrofit wasn't as bad as I thought it would be. I'd say it took me 6 hours total from running the wiring neatly to reassembling the seats, besides the couple days of downtime of waiting for my seats at the Upholstry shop. I never ran into any issues with wiring snce I've wired my (Foglights, Angel Eyes, and Footwell Lightng, Heated Steering Wheel) driecty from the fuse panel so I really didn't expect to have an issue with this.

I hope this write up comes in handy for those who want to attempt this or are in the process of doing it. I so far after only one day of having heated seats hae not one regret about doing this retrofit and yet the heated seats compliment my Heated Steerng wheel as well.

My next mod/retrofit I'm looking into I think would be did you hear Heated Rear Seats!! Just from looking at the heated elements and the looking at my rear seats I know it is possible and would be easier than the fronts haha!!! I knw it would work for sedans, but I'm am ot so sure about the coupes.

And just clarify things there really is no weight difference noticable at least between regular manual seats and heated seats. They both weigh roughly the same still pretty heavy if you ask me. It's when someone with Heated/Power seats comes into play now those suckers are heavy.

Any comments/questions feel free to contact me and even if your in my area and want to do this retrofit I would be willing to lend you a hand.

 

When I swapped in my M3 seats I pulled the entire seat with rails out, just unbolt the one bolt that holds the seat belt end to the outboard rail - that way you don't have to disassemble the rail in the car as I noticed you did.

The seat belt tensioners (the buckle end of the belt) don't have to be changed. Just disassemble the yellow underseat connector attached to the seat by pulling off the black cover (slides off one way) and then the individual plugs for the seat belt tensioner circuit, power adjustments and heating can be removed from the "master" plug and swapped out as needed. I had to do this with my M3 seats as well since the new tensioners had different wiring so I had to reinstall the old ones to keep the airbag computer happy. BTW, that tensioner is an explosive, so be careful with it.