I've got the heated mirror/powered mirror/puddle lamp combo too.
But if I was to try to add heated mirrors, I'd first open up the mirrors and check out the wiring harness. There might be already be wiring and connectors.
I'd also get a Haynes or Chiltion's manual and check the colors of the various wires. This might tell you if there is already wiring to the rear defroster in place.
Years ago, you didn't get anything you didn't order with the car. But the Japanese started putting all the miscellaneous hardware and wiring the factory or dealer *might* need, in all cars. Maybe Ford got a clue.
But if you find that out, you may save yourself a of time, not to mention blown fuses.