I just did this on the driver door switch, but I’m actually looking for some smd LEDs, as I don’t love the light output from the standard ones shining through the little holes. Unfortunately, I didn’t keep track of which were negative leads, but I also had some difficulty. Keep in mind though, 2 of those LEDs won’t light up by just applying power (acc), because one is a window lock, and only lights when the switch is depressed, and the other is the folding mirror light, which I think only illuminates when the vehicle is started. Good luck!
and I just realized you’re talking about the seat heater, and not the windows. Lol. Well, there are several amber LEDs in that one that won’t all light up at once. I’m not planning on swapping those LEDs (presumably smds), only the ones that light the panel. Which ones are you converting?