The official notice
Defect
This recall is for certain integrated trailer modules that were installed before delivery or purchased from a dealer as an aftermarket accessory. On certain vehicles, a software problem with the integrated trailer module (ITRM) may cause the trailer lights not to work when towing. This problem could also cause the trailer brakes not to work on certain vehicles. Note: This problem would cause a "Trailer brake module fault" message to be displayed and turn signal telltale to flash rapidly.
Safety Risk
Trailer lights that don't work could make the vehicle less visible and cause following drivers not to recognize that the vehicle is braking or intends to turn or change lanes. These issues could increase the risk of a crash. Additionally, a loss of trailer brakes could increase the risk of a crash.
Remedy
Ford will notify owners by mail and advise you to take your vehicle to a dealership to update the ITRM software.