I replaced my factory horn as it was all rusted out. I ordered one ( https://www.amazon.com/HELLA-011225921-Black-Trumpet-Horn/dp/B01EG18JX8 ) with the Ford multi-accessory plug on the ends, so I can actually plug my stock harness off the car into them (or at least one of them - both the low and hi horns have the same connector, and I only have one harness coming off the car, so eventually I was going to order another connector and splice it into the original connector). I do not see any cut wires under the dash at all, the horn gets power with a test light both on the horn connector and off the relay box directly. I have switched the relay out with others to make sure I don't have bad relays. No go..the horn will not sound in panic or if you hit the horn button.

So if I'm reading this right - you can skip tracing the cut wires down, by using this relay adapter - you put the open cables into the slots in the junction box for the relay? Then splice the horn wire into whichever of those couple cables in the junction box, is hot? And it will ground out the horn so it works?

Holy shit you just saved me so much time.