Hello PNz,
I know this is a very old post but hopefully you did find the problem here. I have done the same thing, upgraded to Heated Leather Seats and bought the AC/Heat Control Module with the heated Seat buttons. The Seats are installed and my 2007 Grand Prix already has the fuse in place. When I selected the heated seat button the 2 leds go red for the blink of an eye and out.
Not sure what is wrong, maybe I am missing wires in the main cables connecting to the bottom of the heated seats??

Would like to know if you solved problem. Thanks.