When I had that problem last fall, I found that when I had had the seat off and put it back on I either didn't get the seat heater connector connected all the way together or else forgot to connect it at all. Either way, when I pulled the seat off again, I found the connecter was appart. It stops the seat from heating along with the grips.
KC might have hit that one on the head. The seat does have an ambient temp thermostatic cutout on it, but the grips don't; they will come on at any temp. If both are not working and the fuses are good, it's a connection somewhere.