In my 440, the passenger heated seat works, but the drivers one doesn't.

The lights on both switches light up when pressed.

There is power at both of the switches.

I checked the connectors under the seats, and there is power on the passenger side, but not on the drivers side.

So... where should I be looking to try and fix this? Might it be something actually in the seat, and if so, how do I go about getting to it?

Or am I missing something obvious?

it depends how old the car is, it could well be a connection somewhere, but with the heated seats its by far more common for the heater element to break., check the continuity across the connector - seat side, if there are a few ohms there then the element should be ok, if not the element has broken.
Grendel

Thanks. i hadn't thought of trying that.

Will give it a go tomorrow.

there are two elements in the seat with one in the back and one in the seat.If you have an electrical tester then set it to the beep setting and put one conector each side and see if it beeps.
The pads are a continuos line and if broken it won't beep.
You can change the pads if they are broken but it is a lot of work for what is not that important.you have to take the seat out and strip it down and then fit new elements and then rebuild.
hope this helps you.