Heated & Cooled Seats Retrofit – Factory Control Integration + Resistance/Voltage Data Needed

[reyokonova]

Hey all,


I’m in the middle of a heated/cooled seat retrofit and hoping someone with experience in the factory systems or previous retrofit work can help fill in a few gaps.


Truck: Ram (originally equipped with heated seats & heated steering wheel)
Seats: Full Katzkin leather set w/ heated & cooled modules


The factory heated seat modules and wiring were retained, but I sold the old seats. My goal is to fully integrate the Katzkin modules with the OEM controls so everything works seamlessly—heated/cooled functions, level indicators, etc.—without having to hack in aftermarket switches.


Current Plan:

• Use relays or possibly a Raspberry Pi to intercept/translate factory outputs to the Katzkin modules.
• Simulate OEM loads (dummy resistors) so the BCM doesn’t throw errors or disable functions.

What I need from anyone with access to factory heated/cooled seats or understand there of:
Resistance readings for:
 • Heating pads (upper & lower)
 • Thermistors (likely NTC – Negative Temp Coefficient)
 • Ventilation fans



Voltage/PWM data for the factory seat heat/cool control outputs. Does the factory module deliver PWM or simple variable voltage (0–12VDC) for pad and fan control?


Any known strategies for fooling the system into thinking OEM components are still present—e.g., dummy load values, bypass methods.


Findings so far:

• Thermistors appear to be NTC. Charts for similar setups suggest a 10kΩ resistor simulates ~room temp.
• Upper pad resistance: ~3–4Ω | Lower pad: ~2–3Ω
• Fans: <2Ω, likely controlled via variable voltage rather than PWM. No dedicated temp signal for fans—they seem to engage as long as a load is present.

I’ve already enabled heated/cooled seat support in AlfaOBD, and the modules power up. Now I just need real-world resistance/voltage data from factory seats to finalize the integration.


Any data points, wiring diagrams, or firsthand retrofit experience would be greatly appreciated.

So far @SitKneelBend is helping but does not have the systems i need to get readings from thanks Nick.

 

[SitKneelBend]

Hey all,


I’m in the middle of a heated/cooled seat retrofit and hoping someone with experience in the factory systems or previous retrofit work can help fill in a few gaps.


Truck: Ram (originally equipped with heated seats & heated steering wheel)
Seats: Full Katzkin leather set w/ heated & cooled modules


The factory heated seat modules and wiring were retained, but I sold the old seats. My goal is to fully integrate the Katzkin modules with the OEM controls so everything works seamlessly—heated/cooled functions, level indicators, etc.—without having to hack in aftermarket switches.


Current Plan:

• Use relays or possibly a Raspberry Pi to intercept/translate factory outputs to the Katzkin modules.
• Simulate OEM loads (dummy resistors) so the BCM doesn’t throw errors or disable functions.

What I need from anyone with access to factory heated/cooled seats or understand there of:
Resistance readings for:
 • Heating pads (upper & lower)
 • Thermistors (likely NTC – Negative Temp Coefficient)
 • Ventilation fans



Voltage/PWM data for the factory seat heat/cool control outputs. Does the factory module deliver PWM or simple variable voltage (0–12VDC) for pad and fan control?


Any known strategies for fooling the system into thinking OEM components are still present—e.g., dummy load values, bypass methods.


Findings so far:

• Thermistors appear to be NTC. Charts for similar setups suggest a 10kΩ resistor simulates ~room temp.
• Upper pad resistance: ~3–4Ω | Lower pad: ~2–3Ω
• Fans: <2Ω, likely controlled via variable voltage rather than PWM. No dedicated temp signal for fans—they seem to engage as long as a load is present.

I’ve already enabled heated/cooled seat support in AlfaOBD, and the modules power up. Now I just need real-world resistance/voltage data from factory seats to finalize the integration.


Any data points, wiring diagrams, or firsthand retrofit experience would be greatly appreciated.

So far @SitKneelBend is helping but does not have the systems i need to get readings from thanks Nick.
View attachment 569655

There might be target values in the BCM logs for those voltages (might need to enable them to see). They might actually be in the seat modules themselves though.

 

[Mpgrimm2]

This may help....
Jared4.7 's heated pad/element replacement thread and my resistance check notes.
.

 

[nlambert182]

I don't think a Pi or similar is the right answer.

That's a lot of overkill to control a module and you'll need to understand Python programming to get it to work. Since you're just wanting to use the factory switch to control an aftermarket module, you could use a microcontroller (such as a Pi Pico or Teensy 4.0). Those will generate the PWM signals and can control relays and MOSFETS. But... a Pico can only handle 1.8-5.5v, and the heater will need 12v and somewhere between 3-10A. You'll need a relay capable of 12v and +10A to switch the 12v current, and then a diode to protect the Pico from voltage spikes. You'll also need to power the seat heater modules independently of the Pico. You'll still need all of the above if trying to use a Pi, just less programming.

 

[reyokonova]

This may help....
Jared4.7 's heated pad/element replacement thread and my resistance check notes.
.

Thanks alot this gives me what i need to start ill let you know what i find out

 

[reyokonova]

I don't think a Pi or similar is the right answer.

That's a lot of overkill to control a module and you'll need to understand Python programming to get it to work. Since you're just wanting to use the factory switch to control an aftermarket module, you could use a microcontroller (such as a Pi Pico or Teensy 4.0). Those will generate the PWM signals and can control relays and MOSFETS. But... a Pico can only handle 1.8-5.5v, and the heater will need 12v and somewhere between 3-10A. You'll need a relay capable of 12v and +10A to switch the 12v current, and then a diode to protect the Pico from voltage spikes. You'll also need to power the seat heater modules independently of the Pico. You'll still need all of the above if trying to use a Pi, just less programming.

Ya I was just using that as a example your idea is better

 

[reyokonova]

Ok so first round of testing dun I was able to trick the computer with a 7.5 ohm 100w resister and a variable resistor for the temp sensor I also validated that the aftermarket temp sensore also worked and found that the the temp sensor is a safety not controll varieng the resistance does not change the voltage output till it gets to low or high then it just errors and shuts off so on high it put a steady 2.1 volts and and on low 1.1 volts still need to figure out the cooling but this is half the battle I've also verified the aftermarket seats are controlled by a momentary switch 1 click on 1 click medium 1 click low 1 click off with corresponding lights so next will be to use a pie or Pico etc to take 2.1 volts on heat mean close/open relay 1 tim verify power on signal wire for high then 1.1 volts open/close relay 2 times for low verify signal wire for low has voltage then no signal cycle relay again till no signal from seats is present or something for similar so I'm stoked that this will work

 

[reyokonova]

Ok so first round of testing dun I was able to trick the computer with a 7.5 ohm 100w resister and a variable resistor for the temp sensor I also validated that the aftermarket temp sensore also worked and found that the the temp sensor is a safety not controll varieng the resistance does not change the voltage output till it gets to low or high then it just errors and shuts off so on high it put a steady 2.1 volts and and on low 1.1 volts still need to figure out the cooling but this is half the battle I've also verified the aftermarket seats are controlled by a momentary switch 1 click on 1 click medium 1 click low 1 click off with corresponding lights so next will be to use a pie or Pico etc to take 2.1 volts on heat mean close/open relay 1 tim verify power on signal wire for high then 1.1 volts open/close relay 2 times for low verify signal wire for low has voltage then no signal cycle relay again till no signal from seats is present or something for similar so I'm stoked that this will work

 

[reyokonova]

does any one know if the stock seats also turn on the ventilated fan when in heat mode like my aftermarkets do if it does this is even simpler but i need to order the module that has cooling before i can find out for mysel

 

[nlambert182]

Thanks alot this gives me what i need to start ill let you know what i find out

I'd go with the Teensy board over the Pico if it were me. We have found that it is much faster and is more capable than the Picos.... And we're talking $5 for a Pico and $20 for a Teensy (which is made in the USA, btw...).

 

[itswiggs]

does any one know if the stock seats also turn on the ventilated fan when in heat mode like my aftermarkets do if it does this is even simpler but i need to order the module that has cooling before i can find out for mysel

Did you ever figure this out? Still wanting to get my rear heated/ventilated seats working in my 4th gen. Seeing how you got yours to work and maybe take a page from your book…

 

[SitKneelBend]

Did you ever figure this out? Still wanting to get my rear heated/ventilated seats working in my 4th gen. Seeing how you got yours to work and maybe take a page from your book…

I Believe he did but I'll let him answer.