I am not sure of the current draw on these horns, do you have any info on them other than 12 volts ?
Run a fused wire from the battery to a relay, pin 30.
Continue the same gauge wire from pin 87 to the horns.
To actuate the relay with a button, run a fused wire from your circuit panel, to a switch, to pin 85 on the relay.
From pin 86 run a ground wire.
When you throw or press the switch the horns should blow.
All components, especially the wire should be gauged for the total amperage of the circuit.
Use a four pin automotive relay of at least 30 amp rating, (higher if the four horns need more current) standard size for most automotive applications. If you use a five pin relay with pin #87A, it will be hot with 12 volts when the horn is not working, so it will need to be covered with heat-shrink or something may short on it.
The horn switch can be lower amperage, the wire can be 18 or 20 gauge maybe smaller dependent on the amperage draw to actuate the relay. I use 16 ga on all my relay actuating wiring because I have access to it but otherwise I would use a smaller gauge wire.
Fuses need to based on the amperage draw of the horns and the relay actuation amperage, check out the standard fuse in your truck and then double it for the fuse from the battery.
Make sure your wiring is based on that same amperage rating, if a short occurs the wire needs to carry the full current until the fuse blows, eliminating a chance of fire.
I hope this helps some and not confusing.
If you have any more questions just ask… !