Easy enough to test all functions.
To make sure you don’t have a defective horn, connect a ground wire to the case, and a power wire to the connector, and put both to the battery.
If the horn doesn’t honk, then there is something wrong with the horn because you just ran it direct.
Of course make sure that the ground is on a good point, but the test should be fairly certain.
Disconnect the plug from the relay, and with your voltmeter, check the yellow wire for power.
It should have virtually the same power reading as your battery.
With an ohm meter setting, check the wire to the steering wheel and have someone push the horn button. You should see, the needle or numbers, react and resistance should go to zero when the horn button is pushed.
And finally, if the horn is tested good, bolt the horn down to the body, connect the wire, and apply 12 V directly to the horn wire at the relay connector.
If the horn does not honk, then the wire is suspect. But make sure that everything grounds to the body properly.
I see paint everywhere unless you’re Bronco was originally black. With the battery disconnected remove the regulator and clean a grounding point, remove the horn relay and clean the grounding point, and any other grounds that ground to the body.
Or at the very least, unscrew the attaching screws and screw them back in. That should serve to clean the threads at least.
