The contact owns a 2017 Ford F-150. The contact stated that while driving at various speeds, the transmission unexpectedly downshifted, causing the vehicle to abruptly decelerate and shut off. After restarting the vehicle, the failure was self-corrected; however, the failure later reoccurred. Additionally, during the failure several unknown warning lights illuminated. The vehicle was taken to the local AAMCO Transmission Service Center who diagnosed that the transmission wiring harness was faulty and needed to be replaced. The wiring harness was replaced, and the vehicle was repaired. The manufacturer and local dealer were notified of the failure, but no assistance was offered. The failure mileage was 125,000.