My heated seats in my 1990 300E have not been working. The switch light up on both hi and lo on both sides but no heating at all. I have been thinking maybe the seats have been replaced with ones without heating? Seat heating is factory installed on the car.

Today I looked for maybe a non connected cable underneath the seats but found none. Did some research and found reference to the external fuse box. It is located right in front of the fuse box near the strut tower. It doesn't look like a fuse box - more like some kind of relay. But it pops open and it revealed lots of green corrosion, one burnt fuse and one missing fuse...

I cleaned it, replaced the fuses and, lo and behold, both seats heat up! Next question will be why it has been sitting like that for many years? Guess I will find out eventually...

Just thought I'd post this as I haven't seen to much reference to this. I have a photo but I can't seem to upload it from my phone here.

Looking forward to Norwegian winter - Lars

Thanks for this info. I've thought about retrofitting heated seats to my car but it sounds like it would probably be a huge hassle.