My neighbor's truck alarm has been going off every now and then. He is going away for the weekend and wants me to watch it.

My suggestion was to disconnect the horn. I know some vehicles have a simple plug. Any ideas as to this one?

Disconnect the battery. It might reset whatever is wrong with the alarm system who knows.

I would assume the horn(s) has a connector on it that you could just unplug?

I have the same problem with an Explorer. It was easier to pull the two horn fuses than get to the horns themselves. Fuses were red, ten amp. I'd expect an F150 to be similar.

There's usually a relay or something for the horn in the fuse block under the hood. Pull it.

Or cut the power to the horn.

If you like your neighbor, insert an inline switch or a set of crimp on insulated connectors into the power lead. Alternatively, pull the relevant fuse.

If you don't like your neighbor, jumper the horn power lead to ground. This will blow the relevant fuse in the circuit the next time it goes off. Remove the jumper before he gets home.

If the horn is accessible (behind the grille or bumper), disconnect it or them at the source. Or pull its fuse or relay.
The trouble here is that Ford doesn't label them, but it might be found in the owners manual.

Can always try a 9mm universal remote control wrench.

It's not the weekend yet.

Tell the owner, "Sure, I'll watch the truck. If you disconnect the horn first."

In other words, make it his problem.

What Joel said.

Or if it goes off, start pulling fuses.

Connect the horn to the brake pedal before he comes back