Take a look at this and see if it helps:
https://www.wildhorses4x4.com/downloads/WH/Turn Signal Wiring 06_30_08.pdf
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I'm going to assume the horn works?
You could test by running a jumper from the battery directly to the horn terminal.
If that checks out, verify:
* Do you have 12v+ on the yellow at the horn button?
*When you push the horn button, do you have 12v+ on the blue / white under the dash?
* Do you have 12v+ at the wire where it connects to the horn?
You may want to improve (shrink tube / reterminate) some of those connectors. I see metal exposed which could short against... everything in a Bronco.
Can't entirely make it out, but at the left hand side in the middle, there's some white "tape" that looks like it has burn marks too?
I would encourage you to take the time and make sure all of the wiring is in good shape. And if it is not, consider replacing the harness. A good harness is not inexpensive... But a lot cheaper than another truck.
Let us know how it goes!