http://forums.vwvortex.com/showthread.php?2988358-DIY-Heated-seats-for-cars-not-pre-wired!!
Shazam
The above schematic does NOT use the thermostat in the seats through the switch!
In an OEM setup, you've got the switch, which I think is just a rheostat, then a pair of relays behind the passenger rear door card that have some clicky action and a bit of magic inside them, then on the seat is a 6pin connector. +/- for back heater, +/- for butt heater, then the third pair of pins is for a thermistor that, along with the switch in the dash makes the fancy relays go clicky click.
I believe you're still planning on using aftermarket seat heaters? Make sure that first they have built in thermistors or something else along those lines and second, that with the switch you have, the resistance is low enough to get enough voltage through to trigger the relay. Don't run your power straight through the switch, it'll probably burn it out.
A few more things I just noticed about the schematic in the link up top, the relay, "30 unswitched power" is constant 12V, and "75x switched power" is your load reduction relay. I wouldn't worry about it running through your load reduction relay, just shut them off for a cold start, but I would run them off of the ignition so that you can just normally leave the seats on all the time