You should find it attached to the rear of the "change cup" that is near the top of the dash. See page 14 of this Ford Body Builder Advisor Service document
. Note: The view is from the "inside" of the dashboard, looking towards the rear of the vehicle.
I strongly recommend leaving the Ford factory wiring and connector intact. Tekonsha sells a plug-and-play harness for this connector, the 3034-P (link here
). If you have a Tekonsha brake controller (the P3 is a popular model, link here
), it will be a 10-minute installation, with no wire splicing required. If you have a different controller, you can remove the Tekonsha connector from the 3034-P harness and wire that to the controller. In both cases, you will not need to cut into the Ford factory wiring or connector.