Check owner's manual.
If you don't have one copy and paste link below;
www.fleet.ford.com/maintenance/owners_manuals
The horn relay will not be in the owner's manual. That is a dumb answer.
The horn relay is behind the duct above the glove compartment.
Relay being activated
The 2005 Ford F1 50 flasher relay switch is located below the dashboard on the drivers side of the passenger compartment. The flasher relay switch should be labeled as such.
check to see if the fuse is bad
Behind the glove box.
Under dash in fuse panel; Relay Switch #2 (On left, second from top)
how do i find the neutral, or clutch switch on a 2003 ford F150?
location pcm relay 2005 ford f150
The 1991 Ford Explorer air conditioning relay switch can be found on the firewall in the engine compartment. The air conditioning relay switch will be on the drivers side of the firewall.
On the passenger side fire wall in engine compartment !
$10.49 What about it?
There are images available online to help you see where the Fuel reset switch on a 1986 Ford F150 is.
on the fuse panel under the steering colum