Factory heated seats in w123 ... anyone know about them?
 

So, after not having a big project in a while, I have finally started taking apart the 78 240D for a restoration that I hope will not devolve into a part-out. I finally (only took me 10 years) learned to weld and once I finish my MIG class and do a little practice on body scraps, I plan to address the rot on the car ... another thread on that down the road.
My mini-project for now is I would like to rebuild the driver's seat and hopefully return the factory heated seats to function. Kind of putting the cart before the horse but even if I never finish the car I want these seats for something.
Has anyone actually worked on or disassembled the heated seats and circuit from an early 123? Or better yet have a wiring diagram? I only have the Haynes diagram which does not include heated seats, and Google searched have not been fruitful. I'm assuming I can just take it apart and figure it out as I go, but I'd rather know what I'm looking for ahead of time if possible.
I have never tried the seats. When I bought it, the seller told me he didn't use them because when you turned it on, the radio shorted out. I have since found the driver's heat element was not plugged in under the seat, and the wiring from the bottom cushion to the back cushion is chopped in half.
I may just have to trial and error it ... fortunately not much electrical in this car so maybe it will be obvious when I pull the console out. Nonetheless I'd appreciate any input or troubleshooting tips. If not I will try to document what I find for future reference. :)

That is a cool feature! I want to add them, even grabbed factory w126 seat heater switches to install.

The main issue with seat heaters, from the little I have read, is that the elements burn out. The seats take a lot of abuse and usually the thin elements sewn into the seat skins don't last.

Before you try to fix them, take an ohm meter and measure the elements for resistance and if they measure open...well time to move to another project..

Ah bummer ... I suspect that is the case at 367k miles. That makes me a little sad as it's the one thing that makes the car stand out from just another rusty 123, the very rare option (not that it adds value, it's just a fun fact). I will check for resistance though. By the time I finish all the body work (forever) maybe I will be able to source another set of elements. :P

AFIK, there are aftermarket elements you can put in with the stock switches. I've never seen them, but heard about them. I've seen them for sale from time to time and they aren't terribly expensive.

Dkr.

I checked resistance and got .5-.6 ohms on the plug going into the bottom (when putting the meter leads on the wire ... the plug itself was kind of dirty and couldn't seem to make connection), but 5.9-6 at the severed wire going to the back. Not sure what to make of that, maybe the back element is bad, though you'd think it would be the other way around.

.5 ohms is a dead short... don't plug that in...

Don't hold your breath waiting on aftermarket seat heaters that will work with your switches I tried that to no avail for over a year. When a person forgets something in the car ap kneels on a seat to reach it is the death of many seat heaters.

Will the dorman pads work? I've got them in one of my cars, going strong after 2 years of abuse.

http://www.amazon.com/Dorman-628-040-Universal-Seat-Heater/dp/B002U6IL9O

wow... that's a cool kit.

comes with the rings, and the pliers and the wiring and the relay... hard to imagine how you couldn't make those work!:D

I saw a source on youtube that said he fitted newer seats in a 126. Then I remember Roy saying that he's had difficulty getting the newer seats working electrically. Some features can be made to work and later model seats are more comfortable than the early seats but there are now wiring diagrams specific to the seats. Perhaps the same applies to a 123??

I intend to try later models in my SDs even if I end up swapping the motors and wiring over from the originals.

I've seen w140 seats in a w126 SEC convertible before, not sure how hard that was, but it looked great. I had the opportunity to sit in some mint w140 seats in my local junk yard before it closed down (the last good one near me *sob*) and I was shocked by how incredibly comfortable they were.

As for the w123, you can fit W126 electric seats in them physically, its just tricky finding a spot for the controls. This would give you electric\heated seats

OK, well that explains that then! What would a good reading be? I haven't tested the passenger seat yet. If the passenger seat tests good, could I put the seat skin from that on the driver's side? If not I will just put them together as is (not plugging in the seats) and forget about it while I fix the rest of the car. If I ever get it driving again I will celebrate by installing aftermarket units if that is indeed possible.

Those look pretty nice and not very expensive ... Looks like they may fit right up to the wiring that's in there.

I don't know, it depends on the wattage... Likely around 6 or 10 ohms... .5 is likely just the resistance in the wires and probe... A glow plug has around 1 ohm... Ya don't want THAT much heat on your seat!!!