I had a 2015 F150. I plug into my trailer electric with the truck running and the up/down toung jack will not work. With the same trailer I conect it to a new, 2016 F250 and it works. I now buy another F150 2015 and plug it in and it does not work. Does the 2015 F150 not come with the ground or constant 12 volts hooked up? Anyone else have this experience?

 

You need to look under the bumper at the 7-pin connector, and see if the black wire is hooked up. If it is not wired in, look in your manual for the VBATT to the Trailer fuse (maybe called "Trailer 12V" or "Trailer Power"). Every connection to the trailer connector is fused.