Curious,
As others have mentioned, the 110 AC outlet was a power point, probably not provided by the Ford factory for the Expedition before 2011. Also, it was not available on the 2011 Expedition XL (Rapid Spec 101A) or XLT (Rapid Spec 200A). However, it was included with the 2011 Expedition XLT Premium (Rapid Spec 201A), Limited (Rapid Spec 300A) and King Ranch (Rapid Spec 400A) packages.
As a factory accessory, the power point is limited to 150 watts and provides power whenever the vehicle ignition is in the ON position AND when the power point green indicator light, located in the top left corner, is steadily ON. If you overload, overheat or short the power point, it will switch to a fault mode, showing a blinking green light. Then you could reactivate it by removing the item plugged into the outlet, turning the ignition back off, and then to the ON position. The power point may not work properly if you try to power a cathode ray tube type television, motor loads (such as vacuum cleaners, electric saws, power tools or compressor-driven refrigerators), devices that measure precise data (medical equipment), or items requiring extremely stable power supplies.
I have most often used the AC outlet for a phone charger when the other power points are already occupied. No, nothing hangs from my 2011 Expy’s trailer hitch. Just trying to help.