The Canadian SVXs had heated seats as an option.
The US Spec SVX does not have any of the harness on it. You need a complete kit.
http://www.heatedseatkits.com/products.php
You could order the Subaru OEM heated cushions:
Front Left Seat Cushion 64225PA020
Front Left Seat Back Rest 64225PA030
Front Right Seat Cushion 64225PA000
Front Right Seat Back Rest 64225PA010
and build your own harness, but in my opinion, the aftermarket kit is the way to go.
Doug