I too notice that there is a wiring harness that seems out of place under the front seats on my basic X Forester 2004 5 speed. Could it be that car companies actually save money by installing the element in the seat, along with the wiring harness and relay (maybe under the dash near the fuses) when the basic car is put together, then if you want and pay for the option, the dealer just installs the switches? The element itself is probably a trivial cost compared to dealer tech time.
I don't know whether I would hook up 12V directly to the harness connector while the seats are in the car, who knows what other electrical parts could fry But it seems like it would be a pain to take the seats out to do so on a workbench. I wonder if taking the fabric off the seat would be any easier, just to see if there is something that looks like an element underneath.
Does anyone have the part number for the 2004 Forester seat heater switches? I want to try hooking it up to the under-seat harness but would prefer not to let the Subaru dealer gouge me...maybe an aftermarket purveyors of OEM parts or a used parts dealer could find it for a lot less.