I have used aftermarket heaters in a 2000 MB when both died. I couldn't remove the factory heater as they are sewn into the leather cover, so I placed them directly on the seat foam.

I wired them directly to the existing circuit using the connectors from the factory heaters and some time with a soldering iron and heatshrink tubing.

They worked perfectly, but did not heat up as fast as factory due to the layers of material it had to go through as also didn't extend very high up the back or the thighs as they couldn't be placed on metal and the MB seat uses metal straps to hold the seat foam on.

It was about a $100 job in total using my own labour.

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Dan
2007 X3 3.0si*titanium silver*black leather*steptronic*premium*comfort*activity*m sport*bluetooth