Heated Seats Using E46 Retrofit Loom

My Zed came without heated seats, and I thought I'd do a retrofit.

Firstly, thanks to Fishy Dave (amongst others) for his details about retrofitting the X3 harness in this thread
https://z4-forum.com/forum/viewtopic.php?f=2&t=83970

The X3 harness (and the original Z4 retrofit harness) are out of production, so after hours and hours of research, I found that the E46 retrofit harness is usable.

This harness has the exact same wiring colours as for the Z4 retrofit instructions, so no need to look up the E46 instructions (I've done it for you and it used different wiring nomenclature.).
https://www.keepandshare.com/doc2/119303/z4-retrofit-heated-seats-pdf-339k

Note that wherever the instructions refer to "Passenger Side", cross it out and write "Right Hand Side" and for "Drivers Side" write "Left Hand Side".

There are actually two E46 cable kits required - the "Wiring Set" 61116930656 (£36 from BMW) and "Wiring Harness" 61116902951 (£7 from BMW).



The "Wiring set" comprises 3 wires, the brown connector block (X1869) which attaches to the back of the centre console switch panel and a fuse. The only part from this kit that was actually needed in my car was the main red/violet 4mm power wire which runs from that block to the fusebox, as all the other parts were already fitted in my car (i.e. connector block, fuse, and the 2 other thin wires which I think are CANBUS related)

The "Wiring Harness" comprises the wires that run from the X1869 connector block down to the seats. There are 3 wires for each side - power, ground, and temperature feedback. The only slight difference between the E46 and Z4 is that the brown ground wire needs a ring connector putting on one end instead of the existing spade terminal.

Here's my guide:

1. Always remember to disconnect the battery before messing with the wiring. especially before disconnecting the seat wiring otherwise you will get an airbag warning light (also reconnect the seat wiring before the battery).

2. Buy a centre console switch panel with heated seat buttons and swap it over with the existing one.
To do this, chock the wheels, put the car into Drive (Automatic) or 6th (manual) and switch the engine off. Disconnect the battery. Remove the screw at the bottom of the ashtray and pry it and switch unit out together, starting at the bottom. Use a soft cloth to protect the centre trim as there are sharp parts on the bottom of the ashtray.


3. As per the instructions, run the main red/violet power wire from the centre console block (X1869) to the fuse box. To get to the fusebox, drop the glove box fully down (2 clips at the top). Unscrew the 6 screws from round the glovebox and remove it. I found I could use a piece of thin coat hanger to help feed the wire forward under the centre console towards the fusebox. The connector on the end of the power wire is not exactly the same as those installed in the fusebox connector block (X9633), but it does the job fine. That power wire fits into the bottom right hole of the bottom right block in this photo:


4. Put the fusebox and glovebox back together.

5. Reconnect the battery as required so that you can move the seat around to get to the front and rear mounting bolts (16mm). Unclip the seatbelt from the shoulder guide and seatbelt floor anchor nut (16mm), this may be a bit easier with the seat partially out. Remembering point 1, disconnect the under seat wiring block (X275 on left and X279 on right) , by sliding the black cover clip to one side then pulling the yellow block out. Place an old towel over the door sill and remove the seat.
.

6. Vacuum the crud (I found a a big beetle, a shoe brush and a VIP ticket to the Empire State Building, - does a previous owner on here remember that trip ?)

7. This is where I deviated from the instructions - as is often the case there is no real need to disassemble more than you need and I found that if I loosened off the sides of the centre tunnel trim (3 screws per side), I could feed the wires up inside it (towards the top) routing to the back of the car then under the carpet, forward to connect up with the existing seat loom. I found removing the knee pad trim quite difficult. You need a really strong plastic trim removal tool and a lot of force. I used some polyester cable braiding to protect the exposed new wires under the seat.
I also used the rear inner seat attachment bolt for the ground wire (10mm ring connector), rather than running it all the way to the front of the car again (The brown ground wire supplied in the kit is quite short anyway). [ Edit: I found an another bolt used for a cable clip under the carpet near the seat runner which I used for the earth instead. I just had to run a nut up and down it to get the paint off it. ]




8. Insert the cables into the connector blocks (X1869 and X275/X279). I found that a paper clip helped to get the smaller cable fitted properly.



9. Buy some heated seats and fit back together, or ...

10. Alternatively, like me and Fishy Dave, pull your existing seats apart and fit some aftermarket heating elements. This I still have to do. The slight snag here is that you will not have the correct connector block on the end of the aftermarket heating element wires to then fit in the X275/X279, so I have had to use 3 pin connector blocks to sit under the seats.
The other snag is that aftermarket elements do not come with the temperature feedback wire. Fishy Dave reportedly used a variable resistor placed between that wire and ground then adjusted it to about 6 Ohms which fooled the control unit into thinking all was OK and got the heat level right. I will go one step further and try a 10 Ohm (at 25 deg C) NTC thermistor and put that in the seat pad to see if that controls the temperature as required.

Hope that helps someone.
I'll report back if I have any useful updates.

Just to add that something that confused me when working this out is that there is no dedicated control module for seat heating, as with most other cars i.e. the centre console switch panel does it all itself.

As I haven't had any replies, I don't know whether anyone is interested in this project, but I've done some more research on the installation of the aftermarket carbon heat elements (mats).

It seems that there was a bit of duff gen, and the NTC thermistor needs to be 10K Ohm (rather than 10 Ohm). This is used to help the centre control unit have a temperature feedback signal from the mat. There is also (what I believe to be ) a built-in thermal cut-out switch in the Chinese mats which I think cuts the currrent if the mat gets too hot. Some people seem to have removed these, but I think I'll keep mine fitted until I've done some more testing.

When it stops raining for a day, I'll connect everything up and report back, hopefully with a warm bum.

Aftermarket element with thermal cut-out at lower left:

Question please to those with OEM heated seats -
Does the seat heating and the lights on the centre console go off automatically after a few minutes, requiring you to switch the heat back on again if you still want it, or does the heating and lights stay on permanently once selected ?

Thanks.

I found this very interesting having done the retrofit myself. Well done indeed for working out another solution!

In terms of how it works, my system definitely doesn’t switch off. So I’m unsure what’s occurring in your setup….

Thanks very much Darkangelv2.

When I was testing the heating elements earlier today I had a variable resistor (potentiometer) to mimic the temperature feedback. I noticed that when I kept it at a constant 10K Ohm the heating would cut off after about 4 minutes. I think this is because the centre console was providing full power constantly which it does not like, so shuts off. So I tried adjusting the pot a little while it was on, and the heating and lights stayed on.

When I installed the thermistor into the element pad all was well when I tested again because, as the pads heat the NTC thermistor, the resistance drops thus the centre console is happy and reduces the PWM current a little.



I have spent all day inserting the pads into just one seat. This is probably the fiddliest job I've ever done on a car and is not for the faint hearted. You also need the patience of a saint (which I don't).

I'll get some photos of the seat dismantling when I've recovered

I guess there was always potential for an aftermarket pad to present some challenges. Glad it suggests BMW have set the controls up to prevent the pad melting through to my backside!

Fair play to you for sticking with it, I’ve never liked the idea of stripping back the seats - is your foam in decent nick?

Yes, the foam is OK. Thanks for the encouragement. One more seat to go !

I always take the minimalist approach to doing stuff and only remove what I need to, not necessarily what the manuals say. The seat back comes off the base really easily, you only need to undo one torx bolt on each side, hidden under the black trim:



The seat leather can be peeled back by unclipping it at the edge and undoing the infamous hog rings





The seat back can be skinned with the help of a trim removal tool.





In the above photo you can see the pre-formed hole in the foam at the bottom of the seat. This is where I poked the heating element wires through. I then had to drill a small hole on the opposite side of the seat back to allow the wires to exit.

Good write up bud

I did a retrofit on my early build prefacelift and was much easier being plug and play- kudos for attempting this!!

Stuart

And your avatar is 100%! Love the Lightning: any connections to it?

Thanks Stuart.

No connection to the Lightning, other than I love to fly and watch aircraft. It astonishes me we were using Spitfires in 1946, yet Lightnings by 1953. Same with Lancasters vs Vulcans. An unbelievable leap in technology.

You'll often find me at the end of Coningsby runway

Rob.

you are a lucky man if you live near there!

agreed- I'm from an RAF family and may dad was WW2 to around '55, the kit they had was epic;

we live at the end of waddington runway so are blessed with the usual heavies here (sad to see the sentinel get pensioned off a while back) and every so often get treated to fast jets- either Typhoons or last week some F-15's

Cant wait for the arrows to relocate here next year!

Stuart

Cool

Back to the topic, while trying to dismantle the seat base I couldn't figure out how the switch cover trim comes off. There was a screw and some external tabs visible, but it just didn't want to pull off. Anyone know how ? (Part 5 in the picture)

Zulu4 said:

Back to the topic, while trying to dismantle the seat base I couldn't figure out how the switch cover trim comes off. There was a screw and some external tabs visible, but it just didn't want to pull off. Anyone know how ? (Part 5 in the picture)

Click to expand...

That piece of trim is a bit tricky. First, release screw from the rear. Then, second, there are two catches hidden to eye that need to be snapped out:
- One at the upper edge just front of the button panel, press upper edge downwards and pull trim out a bit.
- One at the upper edge approx. two inces from the rear, press downward-forwards and pull trim out a bit.
And finally, lever out the lugs at bottom.

If you have access to TIS, document 52 14 040 will explain in more detail and pics.

Thank you very much DMike. Very useful.
I only have access to a few bits of TIS unfortunately, but I googled your reference and found this photo which shows one of the hidden tabs you mentioned:

The rear tab is similar, but angled 45 deg and thus you need to press down and forward there. When I did mine ages ago, I think I had done the bottom tabs first, which gives the trim more play when you undo the upper edge ones.

Pm sent.

Worked nearly all day on the driver's seat. I had a real result since when I started to take the leather off the backrest, I discovered someone in the past had replaced it with a heated seat backrest and cut the wires off, so all I had to do was solder some wires back on.

Then I inserted the aftermarket element into the seat base.
I found I could get the hog rings back in OK at the edges of the seat, but had to use tie wraps for the seam that goes across the seat base.



Here's the wiring all complete with my connector block to the left of the BMW one.



After refitting the seat I went for a test drive with a lovely warm bum and back. I'm quite chuffed with myself. :driving:
And many thanks to the guys on this fantastic forum that helped me do it.

For anyone attempting this, some tips for the hog rings:
To remove them use a pair of long nose pliers , get them inside the hog ring then pull the handles apart to stretch the ring open. Then you can rotate the ring to free it from the seat and leather.
To re-insert the hog ring, set it up so that there is a gap of about 3-4mm, place it into the leather first then, using fingers or pliers, fit it to the seat. Then use the long nose pliers to squeeze the ring closed. (I was going to use hog ring pliers, but the long nose pliers work fine.)

Zulu4 said:

Buy a centre console switch panel with heated seat buttons and swap it over with the existing one.
To do this, chock the wheels, put the car into Drive (Automatic) or 6th (manual) and switch the engine off. Disconnect the battery. Remove the screw at the bottom of the ashtray and pry it and switch unit out together, starting at the bottom. Use a soft cloth to protect the centre trim as there are sharp parts on the bottom of the ashtray.

Click to expand...

Hey! so in testing my seats, i want to be sure that theres no break in the wire before i get a new center switch, as I think mine has failed. Regardless, do you remember which plug was for the heated seats in the switch? my goal is to test continuity on the wire for the places that I can't see and or easily get to, so to use the seat plug and the pin on the connector to test for breaks. Any help you can give would be greatly appreciated!
EDIT: Found via instructions you sent me

@Zulu is possible to show a wiring diagram, even if it is hand drawn?