Ford 2013 Flex Owner's Manual page 260

260
Trailer Brakes
WARNING: Do not connect a trailer's hydraulic brake system
directly to your vehicle's brake system. Your vehicle may not have
enough braking power and your chances of having a collision greatly
increase.
Electric brakes and manual, automatic or surge-type trailer brakes are
safe if installed properly and adjusted to the manufacturer's
specifications. The trailer brakes must meet local and Federal
regulations.
The braking system of the tow vehicle is rated for operation at
the GVWR not GCWR.
Separate functioning brake systems are required for safe control
of towed vehicles and trailers weighing more than 1500 pounds
(680 kilograms) when loaded.
Trailer Brake Controller Connector (If Equipped)
2013 Flex (471)
Owners Guide gf, 2nd Printing
USA (fus)
Towing
The trailer brake controller
connector is located under the
instrument panel above the brake
pedal.