I'm putting a pair of 981 manual sport seats into one of my 928s. This particular pair (unlike the previous 2 sets I've done) happens to be heatbe. The left contacts in the yellow box underneath are for power and ground as that's how I make the power recline work, and the right two contacts are for the back and seat bottom heater 12v connections, likely using the same main ground.

I could wire these to a switch to supply them with power when I want them on, but my question is how does a heated seat regulate the heat. Normally, you have a dash button with a highs and low setting or a rheostat wheel. Does that dash button change the voltage going to the heating elements, so for example it sends 12v on high but only 6 mv on low or is there a thermo sensor that constantly cycles the heating elements on and off based on the setting?

In looking at these seats, does this scoop in the back and the perforated tops also suggest that they are the cooled versions?

 

Very Simple....take the cat, place it in the seat, let it sit there for a few minutes........then, remove cat -----Seat will be heated....(Repeat steps 1 - 4 on other seat.

 

Unfortunately, not my cat. He's the cat at the leather dye place where these seats are being changed to black. Need a new plan.

 

Two wires does not sound right for heated seats. IIRC, my Audis all have six wires for each seat. Power/Ground backrest, power/ground base, two for the thermostatic switch in the base.
Are you sure you have the right plug? Picture?

 

This is a Porsche heated seat plug with the terminals labelled.

 

In the past that's how heated seats worked: You usually had 2 settings and based on that either a lower or higher current will be sent to the heating elements.
The Porsche heated seats with 3 settings work differently:
The best way to explain it is like that.
The computer which controls the heat "flips a switch" and turns the 12V on and then off a couple times per second.
For example:
For low heat it's "ON" for 0.25 sec on "OFF" for 0.75 sec
For high heat it's "ON" for 0.75 sec on "OFF" for 0.25 sec
I hope you get the idea. Can you do this yourself? If you're really good with electronics, why not?

I went a different route:
I put a pair 997 manual heated sets into my 964 and I "McGuyver'ed" the seat heating by using a cheap eBay seat heater kit, something like this: https://www.ebay.com/itm/16110413457...EAAOxyE3pSGOqI
I only used the electronics from the kit and connecting it to the existing heating elements in the seat, I drilled two holes into the "banana" (under the e-brake handle) and put the buttons there
But it includes identifying and cutting the wires between the heating elements in the bottom of the seat and the back of the seat

If you want to go that route PM me and I can dig out my notes from when I did it

 

Ah! So basically a duty cycle.
Yes, the Audi seats have six heating settings versus two. My Miata in on/off. The newer Audi models went to high/low. Clearly a cost saving measure...or related to all the burnt pants issues that VW had.

 

If all else fails, I read Weber makes a flat style propane grill that fits snugly under the seat.
Pretty cat!

 

Thanks for the info.

So, could I just connect a single on-off switch to the heating elements to warm things up then manually turn them off when they're warm, or do they have to momentarily pulse as you describe. I can see them needing to do that if I want to leave them on, but if using them to warm a cold seat would it work? Is there risk in the heaters getting way to hot with a manual setup like this or is the thermo regulator somewhere between the yellow box power connections and the heating elements themselves that would automatically turn off the heaters once the high temperature was reached?

 

As far as I know there’s no logic inside the seat controlling the temperature
i would give it a try connecting 12V to the seat heating elements, but I would measure the Amps it draws with a multimeter
it should draw around 2 Amps give or take. If it’s much higher then I would stop immediately
actually even better : first measure the resistance between the two plugs for the heater, I would expect it to be somewhere between 5 and 10 Ohm
Then you can calculate how much current it should draw
I = U / R, meaning with U = 12V, R = 7.5 Ohm, It should be around 1.6 Amp

 

Super helpful. Thanks. Will be a few weeks before the seats come back from they leather dyer but will pick this back up then.

 

@Petza914 I found something on eBay that might be the solution to your problem.
Search for "Car Driver+Passenger Seat Heated Pad Digital Display 5 Setting Rocker Switch 12V" or "Digital 5 Gear Display Seat Heater Switch 2 Seats 12V for Driver & Passenger"
This looks like a plug&play integrated switch/controller to adjust the heat for two seats with 5 (!) stages
It's only $20, so probably worth a try

 

Great find and for $30 worth a shot - ordered.

Thanks a lot for the follow up on this for me.

I'll figure out how to install it on the spot where my leaking LCD clock that doesn't keep time is located.

And if it works in the 928, might use the same thing in my 997 for the sport seats I retrofitted into it that happen to be heated.

 

Just reviving this old thread.

I mesured the résistance on my heating elements and it is 1,6 ohm

So if we do the calculation it means 7,5 Amps and 90w per Seat.

Do this values seems OK to you or do you think there is a problem ?

 

Sounds about right. Imagine using a 100W light bulb to heat the seat and seat back. The amount of heat would be about right. Also consider the size of the fuse in the seat-heating circuit. Seems like it was 20A the last time I looked.

The resistance will go up with temperature, making the whole thing self-regulating to an extent. That's not enough control for zee Germans, though, so there will also be a thermistor or other sensor embedded in the underlying support material.