I have a 07 f150 and the other night I got in to start my truck and as soon as I turned the key the horn started blowing constantly not beeping a constant sound so I took the key out and nothing I tried the security button And still nothing. I pushed in the headlight control switch to cut the fog lights off and the horn quit. Now every time I pull the switch out the horn blows. I have no idea what to do about this. Can anyone help? Has this ever happened to anyone?

 

It sounds like your headlight lead is shorted to the horn circuit. My guess is that the short would be in the steering column. You need to get a schematic that shows the wire routing and see where the two circuits are in the same area and then go check it. The headlights and horn might also be located closely together behind the fuse box, I don't know on that model, so that might be somewhere else to look for shorted wires.

My old Dodge had a loose screw in the steering column and would honk the horn if I pulled up on the turn signal lever.