How do I tell if my F-150 has a tow package? I bought it used, and the previous owner didnt know.

 

You will have an extra relay box by the factory relays under the hood and if you have an auto it will include a large external tranny cooler. There will also be either a four and three or a seven wire plug(s) on the drivers side frame rail by the rear bumper. These are the trailer wires, they use there own fuses and relays so do not tie into the factory light harness when wiring your trailer. Using the factory trailer harness if equipped will eliminate the need for a heavy duty flasher for the turn signal.

 

^ What he said!
The will also be a connector under the center of the dash and is for connecting a trailer brake controller. The brake controller will control the electric brakes on trailers so equiped. The tranny cooler is visible under the passenger side front, it will be in front of the radiator.