Heated Seats Using E46 Retrofit Loom

[Zulu4]

Thanks for that Usel

When stripping the old heated seat - from the under seat pin connector block did come a green/purple, brown and grey wire that ran up to the old seat heated pad (in the base of the car seat). The aftermarket seat pad only has two cables - one red and one black. I’ve wired green/purple to red, and then brown to the black wire. I had then read to follow the grey wire from the pin connector block towards the seat head pad and add a 10k thermistor to it, then from other end of the thermistor find ground. Apparently this is needed so the stock heating buttons get the right messaging back through the grey cable!?!

Would you know if that sounds right? Like I say, the lights come on and just go off. Reading the fault code is says something like ‘open circuit’

Cheers

It sounds like you are along the right tracks, but because there are various wire colours on cars and different retrofit looms, I'm not too sure what your "grey" wire is.
To try to help, the thermistor needs to be connected between the thin 0.35mm2 wire (which is next to the two thicker heating power wires in the underseat connector block ) and earth.
The thermistor wires are those labelled A14 & A3 (one per seat) with the term "NTC" in the wiring diagram:

https://www.keepandshare.com/doc2/119303/z4-retrofit-heated-seats-pdf-339k

My lights flashed, like yours do when I tried a wrong value resistor in place of the thermistor, which should be a 10kohm NTC type.

 

[PJRHIGH]

Thanks for the input, Zulu4. Glad it sounds on the right tracks.

Do you know much about resistance levels? From the searching up I have been doing, it looks like heat pads should show roughly between 4-6 ohm resistance. The aftermarket one’s I’ve got read at near 40! I have no knowledge on these things (so might validly question why I’m messing :roll: ), but it feels that resistance might be causing problems.

If I can’t figure it out, I’m wondering about trying to detach the heat pads in my old seats and see if can get them in the sports seats.

 

[Zulu4]

I'm not too sure, but I wouldn't have thought the 40ohms would cause your problem as it would mean the current would be less going through your pads and therefore wouldn't cause a power overload and shut-down.
I'd persevere with ensuring you've got the thermistor wired up correctly initially. If you've got an open circuit where your thermistor should be, that would cause it to shut down.

 

[PJRHIGH]

Thanks for that. I’ve just read something about making sure everything is thoroughly insulated, even the ‘legs’ (not sure what they are called) of the thermistor - did you do that? Can see you placed the thermistor under the heat pad, how did you earth it?

I have had a lot of the cables exposed to test, before closing it all up - i.e. thermistor loose under the seat.

Cheers

 

[Zulu4]

I put heat shrink round the legs and pushed it inside the pad so the 'head' touched against part of the heating element.

I ran the earth cables to a bolt on the bodywork near the base of the seat.
As you already have the factory loom in your car you could just tap into the earth wire that is right there for the heating element (i.e. the thick earth wire).

 

[PJRHIGH]

Much appreciated - I’ll replicate that and hope for the best - do wonder if the heat shrink and placement of the thermistor will do it, but worth a go to be thorough.

Whilst my order says 10k ohm thermistor, packaging doesn’t confirm, maybe not sent the right thing……we’ll see. Fingers crossed

 

[Rossi1001]

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

Does that mean my March 2003 build car will be plug and play too? So swap the centre console switch panel and purchase some heated seats and I'm ready to go?

 

[bigwinn]

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

Does that mean my March 2003 build car will be plug and play too? So swap the centre console switch panel and purchase some heated seats and I'm ready to go?

That’s right

All looms in place

I’ve got a load of switches here if you can find the seats

 

[Rossi1001]

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

Does that mean my March 2003 build car will be plug and play too? So swap the centre console switch panel and purchase some heated seats and I'm ready to go?

That’s right

All looms in place

I’ve got a load of switches here if you can find the seats

Wow that is a result, faffing about with wiring is definitely not my thing! I'll add it to the list....