The contact owns a 2017 Ford F-150. The contact stated that while driving at an undisclosed speed and upon activating the rear window defroster, she observed smoke filling the interior of the vehicle. After a visual inspection of the rear window, the contact observed the rear window lower wire cover on fire. After turning the vehicle off, the fire extinguished on its own, after which the rear window shattered. Emergency services were not called. A fire report was not filed, and no injuries were reported. No warning lights were illuminated. The vehicle was towed to the dealer, who determined that the rear defroster wiring had shorted, causing the wiring to catch fire. The vehicle was repaired. The manufacturer was notified of the failure but referred the contact to the NHTSA hotline for assistance. The failure mileage was 106,000.