Well, it ultimately turned out to be a waste of time as I got about two weeks out of this upgrade. But I ordered and fitted a Chinese heated seat kit. I put the switches on either side of the centre control area / footwell sides. The install went without too much of an issue but it took me the guts of a day, both seats out and stripped to a scary level then refitted... the heat was FANTASTIC. Big issue, which ruined them for me, was that they worked when the car was OFF. Very dangerous in terms of running the battery down. The wiring info was hard to understand and basic. The seller didn't speak good enough English to understand what we were asking and at that point, I didn't know enough about electrics or soldering to find a better solution, though I'm sure one does exist. I've debated this on my Avensis, I ordered and even took out the seats last August but decided against it given my issues with the ambient lights at times. The Avensis seats are also a hell of a lot more complicated in how they're put together compared to the DS3. I really-really-really-really want heated seats in my car.... maybe I'll reconsider.