Heating BMW seats (using BMW parts)

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Bmwe39 said:
Wow this is amazing to see that you came back 5 years later and updated this thread!!
Lots of good info in this thread!

I'm trying to get the heated seats turn on when I remote start my E39 528i 1998

I have the same switch with a roller wheel to adjust the heat strength.

I also only have 5 wires at the switch like another poster, not 6. But my seats are heated as well as backrests.

I did some poking with the multimeter.
With car running, started from the key in ignition, I get 12 volts on pin 3.
If I press the button for heated seats, I get 12 volts on pin 5. So I thought all I need is power on pin 5 to heat the seats?

Now what's really weird...if I remote start the car, pin 3 will have no power, but pin 1, which is switch illumination, will for some reason have 12 volts instead of pin 3. Yet the button is NOT lit.

I wired in a relay the following way.

Terminal 85 is grounded by a negative 250mA from the remote module.
The main power on terminal 30 is provided by the remote module output second ignition wire.
Now I used wire from pin 1 on the heated seat switch for terminal 86 on the relay.
So when I start the car, remote module provides constant power to terminal 30.
Negative output from remote module to terminal 85 and positive from wire on pin 1 of the heated seats energize the relay, and power from terminal 30 flow to terminal 87, which is connected to wire on pin 5 of the switch.
I double checked by starting the car this way that wire going to pin 5 on the heated seat switch has 12 volts.

My understanding is that the seat should start heating up but for some reason it doesn't.

Now I have 3 questions as a result.

- Why do I have 12 volts on pin 1 of the switch if I start the car remotely, and nothing on pin 3. However if I start the car with a key, it's the opposite (pin 3 has 12 volts and pin 1 has 0)

- Why are the seats not heating with my setup, I.e. power going to wire 5 of the heating switch.

- Should I just drop the relay and connect the power wire out of the remote starter directly to the wire on pin 5 of the heated seat switch?
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Hey there, Correct me if I am mistaken but you have the output power from the relay terminal 87 going to the pin 5 wire at the switch? Power shouldn't be coming into the switch from pin 5.
The way I wired my switch was also with a relay. I have fused battery power going to relay terminal 30. The output 87 terminal of the relay goes to the heated power input for the seats. Pin 1 on the switch gets power only when the other switches are illuminated, that gets power from a wire that only comes on when the lights are on. Pin 3 at the switch gets power from a ignition activated wire (can me any power source you want really). Pin 4 is grounded so the illumination at the switch works. Now pins 5 and 6 (5 if you just have 5 wires) is the output from the switch, that goes to terminal 86 at the relay. So when the switch wants to activate the seat heat, it activates the relay to send power to the heating elements. Pin 2 is hooked up to the NTC terminal on the seats.
Does that clear anything up?
 
I'm quite confused by what you mean.
The power to the heating element is carried on pin 23 on the seat connector, correct? That pin 23 gets power from pin 5 on the heated seat switch.
So basically I need to provide power to pin 5 to get the seat warm.
But you say
"The output 87 terminal of the relay goes to the heated power input for the seats."
What do you mean by the heated power input?

I just tried wiring power source (ignition wire) directly to pin 5 on the heated switch, without the relay.

Now the seats heat up very fast and warm. I think the relay was eating some of the power and the seats weren't really heating up.
 
Bmwe39 said:
I'm quite confused by what you mean.
The power to the heating element is carried on pin 23 on the seat connector, correct? That pin 23 gets power from pin 5 on the heated seat switch.
So basically I need to provide power to pin 5 to get the seat warm.
But you say
"The output 87 terminal of the relay goes to the heated power input for the seats."
What do you mean by the heated power input?

I just tried wiring power source (ignition wire) directly to pin 5 on the heated switch, without the relay.

Now the seats heat up very fast and warm. I think the relay was eating some of the power and the seats weren't really heating up.
Click to expand...
Hey there,
Yeah I think we are not quite getting what each other means. This statement you made "power from terminal 30 flow to terminal 87, which is connected to wire on pin 5 of the switch" indicated you had the power from your relay going to the switch via pin 5 on your switch which confused me. Pin 5 should be sending power out from the switch to the seats, your statement meant the opposite. Pin 3 of the switch is the one that is technically supposed to get power input and the switch then sends it out via pin 5 to the seats for heating. I am glad to hear your seats are working at least. I think the relay in your wiring was not quite set up right so taking it out solved the problem.
What I meant by "power input" for the seats, was the "hot" terminal (pin 25) under the seats that is supposed to receive the power from the switch (or relays depending on how you wired it all) and that power flows to the heating elements in the seat.

Hopefully that is all clear as mud :hillbilly:
 
I understand what you mean, that pin 5 sends the power out to pin 23 or 25 (don't remember which one) to start heating the seats.
Power comes in via pin 3 to the switch, goes out via pin 5.
The problem for me is, you have to press the switch button for the heated seat so that it sends the power from pin 3 to pin 5.
Unfortunately I cannot press that switch if I'm out of my car and starting it with a remote starter.
That's why I simply provide power directly to pin 5 while the car is started.
I created power on pin 5 and on that wire in a different way, without being able to press the button.
It doesn't really matter that pin 5 is for output of power.
Basically the bottom line is, as long as wire 5 has power, the seats will start heating.
I simply supply power to wire 5 via another wire from the remote starter, until I get into my car. This way I bypass the heated seat switch module.
As for the relay, I'm not sure why it wasn't working. I did measure voltage and I had 12 volts or so going to pin 5 on the heated switch from terminal 87 of the relay.
However now, without the relay, I have over 13 volts coming out of the 2nd ignition wire and going directly to pin 5 of the switch.
I didn't take precise measurements and I don't remember the exact voltages. But I guess a small difference of 1 volt can be enough to heat or not to heat the seats.
I had the same issue on a different vehicle where I was trying to make a heated steering wheel work from remote.
It didn't heat with a relay but did heat without a relay with direct connection.
So I'm thinking that I'm losing some power when my connection goes through a relay.
I just don't have enough knowledge in electronics to understand what's going on exactly.
Well at least we both solved our problems lol.

I saw that you ended up changing your switch from the rotary switch to the one with only 2 settings.
I thought the rotary switch would provide more flexibility and more adjustability for the heating settings? Was just wondering why you decided to switch.
 
Soo, while messing with this, have you guys found a way to power the heat in the seats without any of the BMW switches and tech? Just a 12v to any of the pins?
Maybe I can do a timed relay?
Really don't want all the BMW switches and wiring. Thanks in advance
 
I used bmw switches because they fit in the console coin openings. The wiring would be the same for any kind of switch. The thermistor on my switches let you control the temp. If you don’t care about that, a on/off switch will suffice.
 
red66toy said:
So I ended up switching out the original BMW switches with this different style BMW switch. I like the two settings. The hot setting is "taint tickling good" and heated up fast! I love this upgrade so much. Now if only I could afford heated AND cooled seats, that would be the real bee's knees in these green house cruisers. hahaha
50963084908_25a68b58a8_c.jpg
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Just about to take on a similar project. Are you running the heater power through the switch or through a relay? The wiring to the switch looks like 20 gauge and I can't imagine it could handle 7-10 amps.
Thanks!
 
NoLys1776 said:
Just about to take on a similar project. Are you running the heater power through the switch or through a relay? The wiring to the switch looks like 20 gauge and I can't imagine it could handle 7-10 amps.
Thanks!
Click to expand...
Running through a relay. I agree on the wire size. I just felt better using a relay. :)
 
red66toy said:
Running through a relay. I agree on the wire size. I just felt better using a relay. :)
Click to expand...
Thank you for the reply! Excuse me if I missed/overlooked this part of your wiring but I can't figure out how the NTC wire would influence the output of the relay.
If the switch is hooked up to the coil side of the relay and the heater power runs through the contacts of the relay, does the NTC line signal the switch to disengage the relay?
Again, thank you!
 
NoLys1776 said:
Thank you for the reply! Excuse me if I missed/overlooked this part of your wiring but I can't figure out how the NTC wire would influence the output of the relay.
If the switch is hooked up to the coil side of the relay and the heater power runs through the contacts of the relay, does the NTC line signal the switch to disengage the relay?
Again, thank you!
Click to expand...
The NTC wire is hooked up to the seat and tells the switch when the seat is too hot. The switch cycles the heat mats on and off with varying frequency. The NTC signal wire doesn’t directly go the relay. Just tells the switch to not cycle the heat too much and risk a fire.
 
red66toy said:
The NTC wire is hooked up to the seat and tells the switch when the seat is too hot. The switch cycles the heat mats on and off with varying frequency. The NTC signal wire doesn’t directly go the relay. Just tells the switch to not cycle the heat too much and risk a fire.
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Got it, it's an input/feedback wired directly to the switch. Last question is in regards to temp control and the cycling of the heat mats. With the switch output wired to the coil side of a SPST relay, is the switch cycling the relay on and off faster or slower depending on the temp setting? I saw your video and on low it looks like it cycles once every second or so. I'd imagine that would wear out a normal mechanical relay if it's cycling that frequently. I just want to make sure I'm not missing something.
Thank you!
 
NoLys1776 said:
Got it, it's an input/feedback wired directly to the switch. Last question is in regards to temp control and the cycling of the heat mats. With the switch output wired to the coil side of a SPST relay, is the switch cycling the relay on and off faster or slower depending on the temp setting? I saw your video and on low it looks like it cycles once every second or so. I'd imagine that would wear out a normal mechanical relay if it's cycling that frequently. I just want to make sure I'm not missing something.
Thank you!
Click to expand...
Usually high quality relays have a cycle life time in the order of hundreds of thousands to millions. With how frequently and how long a person would use heated seats… I think the relay would last a looooong time. :)
 
red66toy said:
Usually high quality relays have a cycle life time in the order of hundreds of thousands to millions. With how frequently and how long a person would use heated seats… I think the relay would last a looooong time. :)
Click to expand...
Ok. I just wanted to make sure I wasn't missing something and I understood how the mats were being controlled. I think at first I misunderstood how the BMW switches were controlling the high and low and that they DON'T operate like normal toggle switches. Thank you for clearing that up. Time to find my switches!
Thank you for the help!
 
I happened to find a couple different switches but when I turn them on, they stay on for a moment and then turn themselves off. While using one to turn on a relay, the indicator light goes on and I can hear it double click the relay on-off, pause, on-off, pause, on-off and then the indicator light goes off. I've tried two 30a relays and even a micro 20a relay and they all function the same. It feels like it's not running enough current to hold the contacts in the relay and occasionally it will do a rapid-fire on-off. Used two different batteries between 12.5-13v.
Admittedly, I haven't done an electrical project in a couple years so I'm probably overlooking something simple.
Any ideas what's going on, what I should test or how to fix it?
Thanks!
 
20220822_143248.webp

I also tried the same one with the temperature wheel that red66toy used, although that won't even activate the relay.
It's 5 wires
Power, Ground, Output, Illumination and NTC.
 
For the sake of posterity I'll include my findings.
As I understand it, my switches are rear seat switches from a 2004-2010 X3/X5 and I think the 5 series ran them too. I'm also running 2016 F30 seats and my testing is on the Passenger seat.

After a lot of trial and error, no matter how I try hooking things up, the only way I can get the switch to function is to connect it straight to the seat heaters with the NTC connected. I even tried simulating the resistance with a bulb inline with the relay while powering the heaters with and without the relay and having the NTC connected and neither of those worked.
There's something about the heater circuit with the NTC and the switch electronics that won't let it function any other way. I also tried powering the heater module and may still try a few more iterations of that but at least I know my switch works.
On my switches, the Power in is a 12ga wire and the heater out is a 14ga wire. The amperage through the switch and the heaters is 9A on high. I think that 14ga wire will handle it well enough but I'd feel a whole lot better not running 9A through the switch and being able to run a 10-12ga wire to power the heaters.

If anyone can think of a way to get the switches to run a relay, I'd be grateful.
 
As a final note, I've found that the switch will run one heat mat and a relay. In lieu of a better idea, I've decided to have the one mat with the NTC be powered by the switch and have the switch also cycle a relay on the ground side of that circuit. I'll have that relay provide power to the second heat mat. That way only about 5 amps is running through the switch and that 14ga output wire. I know Hella and others make solid state 12v mini relays so I can just tuck it under the seat and don't have to listen to a bunch of clicking. This may be a bit overkill and isn't the most budget friendly solution but I'd rather be safe than sorry and it's not much more work when I'm running the new wiring anyway.
Still open to any other suggestions and thank you all for this helpful resource!
 
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