I would check fuses 18 and 43 in the SJB to see if there are 2 pins where the fuses go or just 1. If there is only 1 It would mean alot more work and that the vehicle is not wired for heated seats.
Pins 33, 22, 27, and 16 on the drivers side seat connector are for the Heated seats,
Pins 23,14, 22, and 16 on the passenger side are for the heated seats.
I would start by checking to make sure the pins are present on the vehicle side of the connectors.