DIY: Complete E36 Heated Seat Retrofit Step by Step

[Turfburn]

Tools list:

The required tools for this project wil be:

TX-47 Torx (male star bit)
T-15 Torx
16mm socket
10m socket
7mm socket
6" 1/4" drive extension
Flat blade screwdriver
Phillips screwdriver
Multimeter (troubleshooting if need be)
Wire Cutter
Hog nose ring pliers and rings
1/4" drive swivel/universal joint
Christmas tree fasteners for seat base:

Factory part number list:
Full Retro fit kit: SPORT: 52 11 9 402 814 BASIC: 52 11 9 402 813

OR by parts only:

Harness: 61 12 9 401 349
Relay:
BASIC:
Seat Heater bottom: 64118391696
Seat Heater Back: 64118391697
SPORT:
Seat Heater bottom: 64118353027
Seat Heater Back: 64118353028

heater switches widely available for about 20 bucks for a pair on E-Bay, so I found it to be cheaper to do this by parts rather than with the kits.

Photos below is the retrofit harness and all it's connectors.

[ttkid06]

cool, would like to see the finish results

[Turfburn]

Removing the seats from the car is very simple. There are four 16mm bolts that hold the seats in to the car. There are plastic caps on the front bolts, so pop those off with a flat blade screw driver, then remove the four bolts. raise the seat to the maximum height, then slide all the way back to get to the front ones and then all the way forward to get to the rear bolts.

Once the bolts are out, you can tip the seat up and disconnect the connectors underneath. Seats without heaters will have two connectors on the driver seat and 3 connectors on the passenger seat. All of them are simple pull connectors with no retaining tabs.

Then use the TX-47 torx to free the bolt off the side to remove the seat belt from the frame. After that, the seats can be lifted out of the car without a problem.

Rear Seat Pad:
With the seats out you can then remove the seat pads. The rear pad comes off very easily. Simply remove the head rest and then the two base screws with the T15 torx. After doing so the back plate will pull up and off easily.

With the back seat plate off, you can then access the hook flaps that tighten the upholstery. Simply pull the upholstery off of each of them, and then the entire cushion can be pulled off toward the front easily.

Base Seat Pad:
To remove the base pad, simply locate the 4 christmas tree clips that protrude from the base. Two of them are pictured below. Simply cut them off with a wire snips. the hard one that is shown near the torx screw I found was easiest to remove by simply using a needle nose pliers to break it apart, then the seat pad lifted off reasonably easily.

[Turfburn]

With the seat pads removed from the seat frame you can get started on the upholstery. This is actually really easy, as long as you use the proper tools.

I did not need to do the back pads, but the procedure is the same for all of the upholstery.

Removing upholstery fabric:
Start working on the long sides. Use a wire snips to cut each of the hog rings all down the sides. Once those are all cute/removed, then pull out the bracing rod that ran in that direction. This will allow you to work on the other direction by simply rolling the material back. With the bracing rod out, roll back the material from one edge and do the same thing, clip each hog ring until you have cut them all out and the upholstery is free.

Layout Seat Heater:
With the upholstery off, you can then lay out the seat heater. Simply line it up with the grooves in the seat with the little hole punched areas where the hog rings will reach back to the hold down rods. The only thing to pay attention to here is to make sure that connector pigtail from seat heater comes out the seat pad on the correct side so that it comes out by the pass through hole in the seat base as showin in the picture below.

Replace Upholstery:
Once you have the heater laid out, do the reverse directions for placing the upholstery back on. Work down the lateral grooves using the hog ring pliers to place new rings to tie the reinforcing rods down to the hold down rods in all the positions where there were rings before.

Also, do a once over before putting the new rings in to make sure you have all the ring fragments out from cutting them before. If not, they could come back to haunt you later!

Re-Assembly:
With the upholstery back on, and hooked back on to each of the hooks, you can remount the seat back easily. Just reverse the removal steps.

To remount the seat base, snap in 4 new christmas tree clips. But to do this, you have to remove the snapped off parts left in the seat base. The easiest way to this was to push the foam down away from the mount points, and then use a needle nose pliers to grab the edges of the clip and break them off. Once they are all broken off you can pull them out of the base so you can put new ones in. With the new clips in, route the wire through the hold in the seat frame, and then press the seat base back down to lock it down. Your seats are now finished with heater elements installed and you get to move on to the hard stuff, wiring the car.

[Turfburn]

I had found this stuff very confusing based on the other instructions out there, so hopefully this clears some of that up.

I left the seats out for all of the wiring until the final steps. Makes it much easier to access everthing.

I started on the driver's side and that is where most of the work happens.

Remove Dash and coverings:
The first step is to remove the underdash cover and the speaker cover in the footwell to get access to the wiring passthrough. To remove the dash simply remove the 3 screws that hold it by the steering column. One is on the upper left corner, the other is the upper right corner, and the final is the lower right corner. With those 3 screws removed you can then pull it at a bit of an angle to rotate it toward the door opening. Once it is rotated toward the door opening by about 3" on the far away end, pull straight back. This will free the clips and the dash comes out.

To remove the speaker cover, simply remove the screw holding the hood release lever and the 90 degree turn plastic fastener. With those removed you need to get the edge that starts to go under the door sill trim out. After pulling that out, pull the speaker cover and dead pedal assembly straight back and slightly up. This will free the clips on that.

After that is out, take a 10mm socket and remove the 3 small screw from the knee reinforcement panel which is the metal panel with the foam injected in to it. This is a key thing I learned later in the install that would have saved be a TON of time if I had done it at the start!

Pictures of the underside dash screw, the clips on the dash, and the clips on the speaker footwell clips are all below.

[Turfburn]

Four fuse box screws:

With the dash coverings out of the car, you should now have access to the 4 small 7mm head bolts that screw through the firewall to the base of the fusebox in the engine bay. Two of these are easy to get to, and two are a bit harder.

Before proceeding to removing the screws, you need to take down the connector breakout box. This is the black plastic frame that has a huge rats nest of wires going in to it. To remove it, there is a clip tab at the middle of it agains the metal wall. Pull this forward, and then push the box upwards. It should move up about 3/4" and then you can pull it straight away from the wall. It is held in place with keyhole slots that the plastic tabs fit in to. A picture of these tabs is below to make it clearer.

With the breakout box removed you can now see all the screws, the screws are in anevenly spaced in a square pattern. The first one is open and bare and is the lower right corner of the pattern. The second one is behind the wire harness at the lower left. Turn the wire harness hold clip 90 degree and you can move the harnesses out to get to that screw. The third screw is the top right and there is a round cutout in the sound deadening material that should give you access to it. The fourth screw is in the upper left corner and should have a similar access hole through the material to get to it. However I couldn't see the hex head through that. I had to cut the material to roll it back to get access to it. Once these 4 screws are out, you are done under the dash... for now.

Engine Bay Fuse/Breakout Box

Moving in to the engine compartment, take the plastic cover off of the fuse box. With the cover off you should be able to locate 4 small T15 torx screws. Two are easy and in the front, and two are harder in the back. You should be able to pull the fuse box up and forward about 1-2" because you have the four screws out at the firewall. With the box forward use the Torx to remove the front to screws. With those out switch to a 6" 1/4" drive extension fitted with a 1/4" universal joint. this is KEY to making this easy to do. With that assembly you can easily get the two rear screws to open up the fuse box.

Once the four screws are out you can lift the carrier that holds the fuses and relays up. I also removed the carrier that held the two big engine harness connectors on the side of the fuse box. You can unscrew the top connectors of those easily, and then there are two tabs near the ends that let you release that carrier and pull it up so you can drop the parts leading into the engine bay down so they don't get in the way.

With the fuse carrier up and pulling on the wires you can now see the pass through guide clamp. This clamp is pinching the foam wrap around the wire harness as it comes in to the distribution box. Pull straight up (relative to the fuse box wall). It took a LOT of force to free it. Also, on the back of there is a plastic tab that is attached to the harness with a zip tie. I broke this off and didn't see any drawback to this approach as cutting that zip tie would be hard to do, but feel free to go under the dash and try to do so!

Freeing Fuses 1-10 carrier
Once that guide clamp is up and off you'll have a little more room to work. With this room identify the fuse carrier for fuses 1-10 (reference the fuse box top cover for a diagram). Then remove fuses 1 and 2, and you'll see why in a second.

To remove the fuse carrier there is a tab on the bottom side. Pull that back and push down on the fuse carrier from the top at the end by that tab you pushed back. It'll go down about 1/4" relatively easily. After that, well, brute force is your friend here. There was no other method that I found. Just push on that end hard, basically the end rotates down and past the tab you are holding back and then the carrier pops out once it gets down far enough.

Connecting fuse wires

With the carrier out, you are ready for some wires! On the retrofit harness you'll find a green w/blue striped wire, a red w/purple striped wire, and a red wire that has two ends on it attached to the red w/purple wire. I zip tied these 4 wire ends together and passed them through the firewall up in to the fuse box. once these are there, you can clip the zip tie. (picture of the group below)

Look at the side of the fuse carrier and you'll see a white tab at the Fuse 1 end. pry that straight out gently with a small screwdriver. Then pull the hold white plastic part out. This is a lock/retainer to keep the terminals in the carrier. They stay clipped in on their own, but this is an added measure. Now, locate the position for where fuse 4 would be in the carrier. Then take the red w/purple wire and pop it in to one of the side of the fuse 4 position. Take the red wire most closely bound to that red w/pruple wire and pop it into the other side of the Fuse 4 position. Slide the white plastic carrier back in.

With the wires and white locker back in you can put the fuse carrier back in. Same deal as taking it out. Put the fuse 10 in first and high so you are at an angle. Pull the tab back, and then push like all hell to get it to pop up and in. Once it pops up and in, you can put the 1 and 2 fuse back in, and stell a 15 amp fuse from the fuse cover to put in fuse 4 position. If you get fuses mixed up, look up the fuse numbers on the cover and the amperage, and match accordingly.

[Turfburn]

Connecting "fan connector" connections
BMw uses a ton of these nifty breakout bus connectors that they call fan connectors. If you dig down in your fuse breakout box you'll find a TON of these things floating around loose with wires coming out of them. This was the hardes part to sort out from the factor instructions as they were FAR from clear, but with my pictures and explanation, this is a total cakewalk.

Dig around in that fuse box in the engine bay that you just did the fuse carrier install on. Find one breakout connector that has all green w/blue wires coming out of it with one open space. Also, dig up one larger/longer connector that has all plain red wires coming out of it and should have one spot on it (there are two of these connectors, only one of mine had a spot open). Once you find these, take the red wire you have from the retrofit harness and slide it in to an open spot on the red breakout connector. Match the orientation etc of the other wires going in there. I used a small screwdriver to push it all the way down and seated. Do the same with the green w/blue wire in the connector with all green and blue wires.

Once that is done, push the breakout connectors down into the bottom of the fuse box. I then peeld back the foam gasket tape around the wire harness and pushed the 4 wires from the retrofit harness under the foam tape and then wrapped it back the way it was. once this was done, I pushed the harness down in it's cutout to where it was when I started and then pushed the guide clamp connector back down over it. It took a little force to get that to go down and had to work to get the fuse box firewall gasket over the guide clamp without pinching it.

Closing up in the engine bay:
So now that you have put in the wires for the fuse #4, and put a red wire in to the red breakout connector and put the green w/blue wire in to the green w/blue breakout connector, pushed the breakout connectors back down in the box, covered the wires with the foam tape and replaced the guide connector you can close up things under the hood. Put the 4 torx screw back in to close up the box and then push it back down in to position. Then go back under the dash and put the four 7 mm bolts back in to re-attach the fuse box in place.

Back under the dash
Under the dash go back to the breakout box that you removed from the side wall. Locate the breakout connector that has all grey w/red wires in it. Use a pliers to squeeze the tabs at the top so you can pull the connector out (if you want to make it easier to work with it). With that connector out, locate the two grey w/red wires from the retrofit harness, these are the illumination wires for the heated seat switches. Slide these two connector ends in to the breakout connector just like you did in the engine bay for the similar connectors.

Once that is done, pop the grey w/red wire breakout connector back in to the breakout box. Also, locate the red w/yellow breakout connector from the retrofit harness and also snap that into the breakout box.

Also, on the retrofit harness is a grouping of brown wires with a ring terminal on it. On the side near the breakout box mounting point (see pictures below) there are several other ground connectors attached. Use a 10mm to loosen that nut and then add the retrofit harness grounding group to the ground point and then tighten the nut back down.

[Turfburn]

Illumination Wire Connections

With the ground wires connected and the illumination wires put in place, you can now insert the relief relay into the relay socket on the retrofit harness. On the side of the socket is one set of guides with a locking tab. Slide these guides over the end position on the breakout box (the position that would be most toward the rear of the car when the breakout box is put back). After the relay is on, you can put the breakout box back in its original place.

This finishes up the wiring connections. Now you just have to route the seat heater switch connections and the connections for the seat heaters themselves.

Routing Wires:

I found that the carpet was much too stiff to lift up and really effectively route the wires, so I just tucked my wires down along the side and there were not sharp edges and I felt good about that.

To get the carpet free up you need to remove the side trim. The snaps are pictured in one of the photos below. Just pull straight up with a quick but firm/strong jerk and you'll pop one or two of the snaps and the rest come easy after that. Pull straight and not too close to an end or you will crack the trim. I did that by accident on one, but was able to repair it easily with some super glue and the crack is invisble.

With the side trim off you can push the carpet away from the frame and route the wire down in the crevice about 4 inches or so. Then lift up on the carpet a bit and you can route the connectors underneath the carpet and over the 6 inches from the edge to the cutout where the other seat connectors come up. Once you accomplish that, tuck any excess wire back down, and snap the side trim back on.


Center routing
Before you proceed you'll need to remove the passenger side under dash covering. There are just two screws and this pulls out. Then you can remove the passenger side trim and the passenger side speaker cover.

Next, you can route the passenger side connectors and the heated seat switch connectors. I routed them up along the main harness and over hte steering wheel. I zip tied about every 6 inches to make sure it wouldn't get caught on anything. There should be a smaller wire harness that breaks away from the main harness over the column and passes down between a couple of aluminum tubes for the AC system right along side the center stack. Run the heated switches down along this harness and ziptieing as necessary (after you've completed the run of course). You should be able to fish the connectors through to where the cigarette lighter is. Pop off the shift boot (pinch the sides in toward the center and then pull up and it'll come right out). Then pull up the foam sound deading material. You should be able to get your hand in by the cigarette lighter base. Just push up to pop out the blank covers for where you want to put the switches. I also popped up the AST switch to give myself more room. I felt around until I could find where I had fished the retrofit harness connectors to and then pulled them through as you see in the picture. Don't connect the switches yet though, as you'll need to figure out which is the passenger side and driver side in a little bit.

[Turfburn]

Nearly done!!!

Passenger side wire routing
The last thing you need to do is route the passenger side wiring over. Pass this along the harness over the center tunnel. I zip tied once as it came on to the passenger side footwell. Then I simply pulled the carpet forward and tucked the harness behind the carpet all the way to the corner by the speaker and then dropped it down along the frame to make the run to where it turns and goes the 6" again in to the cutout under the seat. You can ziptie up to the harness under the dash if you want, whatever works. Same deal as before, stuff extra wire down along the frame, make sure you have about 8-10 inches (similar to the other connectors) coming through the cutout under the seat.

You can now put the speaker cover back in and snap the side trim back on. If you are feeling confident you can also re-assembly the passenger and driver side dash areas.

Test Seats and ID switch side
Now, put your seats back in, but don't bolt them down. Connect the original connectors and your new heated seat connectors. Once that is done, you can re-connect the battery in the trunk. Turn the ignition key to "on" and press the high setting on ONE of the heated seat switches. Wait until the switch switches to the low setting automatically and then press the high button again. now touch your hand on each of the seats to see which is warmer. Then snap the switch in to the hole corresponding to the seat that was warm and the other into the open slot. Flip the key off and start closing things up. Re-torque the seats bolts down (HAND thread the rear bolts in as I saw that one of mine had been crossthreaded by someone previously. I had to re-tap and re-cut to fix it). I believe the bolts are torqued to 51 ft-lbs. Also finish up putting back any trim and the center console etc.

That should do it. Enjoy the toasty warmth of your new heated seats!

[Turfburn]

All done! Enjoy, good luck, post if you have questions, and please tow to the DIY forum when appropriate.

Thanks!

[Turfburn]

bump to get towed.

[hellrot98m3]

Tools list:

The required tools for this project wil be:

TX-47 Torx (male star bit)
T-15 Torx
16mm socket
10m socket
7mm socket
6" 1/4" drive extension
Flat blade screwdriver
Phillips screwdriver
Multimeter (troubleshooting if need be)
Wire Cutter
Hog nose ring pliers and rings
1/4" drive swivel/universal joint
Christmas tree fasteners for seat base:

Factory part number list:
Full Retro fit kit: SPORT: 52 11 9 402 814 BASIC: 52 11 9 402 813

OR by parts only:

Harness: 61 12 9 401 349
Relay:
BASIC:
Seat Heater bottom: 64118391696
Seat Heater Back: 64118391697
SPORT:
Seat Heater bottom: 64118353027
Seat Heater Back: 64118353028

heater switches widely available for about 20 bucks for a pair on E-Bay, so I found it to be cheaper to do this by parts rather than with the kits.

Photos below is the retrofit harness and all it's connectors.

hey great wright up, i already have the seats with the heater elements in them and i have the switches. my car didnt come with this option though, which kit would i need and about how much was the wiring harness? thanks

[Turfburn]

Hey,

You should only need the wire harness and relay based on what you have already. Wire harness is about 140 dollars I believe. Relay was like 6 dollars.

Thanks,

Steve

[bonoz]

Nice. Thanks for the write-up. Does anyone know if "memory" seats can be retrofitted as well?

[mijbr90190]

would fitting these in the rear seats work as well. I always thought it would be cool (or hot) to have them back there with oem switches on the doors or by the ashtray

[Joylove]

Does anyone know the part number for the christmas tree clips?

[STe36]

very nice write up

[peterp103]

Where did you find the harness? The PN 61 12 9401 349 doesn't come up at REALOEM.COM .

[xdt]

Back under the dash
Under the dash go back to the breakout box that you removed from the side wall. Locate the breakout connector that has all grey w/red wires in it. Use a pliers to squeeze the tabs at the top so you can pull the connector out (if you want to make it easier to work with it). With that connector out, locate the two grey w/red wires from the retrofit harness, these are the illumination wires for the heated seat switches. Slide these two connector ends in to the breakout connector just like you did in the engine bay for the similar connectors.

Guys, I know it's an old thread, however I need advise on the above information. I am currently installing heated seats in my car but my breakout out connector only has an opening for one of the grey w/red wires from the retrofit harness. Is it wise to splice the 2 wires and install in the connector? If not what are my options? The car is a 4door all power windows, locks etc.

[Joylove]

Yes you can splice them together, alternatively you can check the other side of the car, where there is an illumination splice point also.

[xdt]

Joylove
Thanks for the info, are you referring to the breakout box under the glove box?

[Joylove]

Joylove
Thanks for the info, are you referring to the breakout box under the glove box?

Yes.
There are illum fan connectors in both breakout boxes.

[ke20]

Dont know if anyone can help me here.

I'm instaling heated seats but the ends of the wires were cut! i manage to get everything working with the switch on full power but if i chang to the less heat position they dont work!

[Bio Hazzard]

I didn't know there was a relay required to retrofit heated seats? Is this only for E36s? I'm almost certain that the switches for E39s had electronics integrated into the switch and when it reached its temp it would halt the flow of power to the seats.

[Turfburn]

All the electronics are in the switch, but the power supply and fusing comes via the relay