Funny that you asked, I just went through this issue and resolved it today on my friends 33 Ute. Our issue was that the horns grounded out once they were mounted on the brackets, so every time you connected power to the car, the horns would blow. To use the original wiring we either had to isolate the horns from ground or use a set of relays to make them work properly.
We used two 4 pin relays and hid them in the horn caps.
If you are running an original wiring wiring harness and don’t want to splice into the horn button wire you can try this.
1. Connect the 12V power to pin 30 and pin 86. (Yellow wire).
2. Run your wire from the horn button to pin 85. (Blue wire).
3. Run a wire from pin 87 to the positive side of the horn. (Red wire).
4. You do not need to connect the negative terminal on the horn if the horn has a good ground connection with the mounting bracket. If does not connect the negative horn terminal to a good ground source.
Relays come in many shapes and sizes, so we found this one at the auto parts store. Then we used some electrical tape to insulate the terminals so it would not short out against the horn cap.
I am not an electrical expert, so this may not be the most elegant solution. Hope this helps, good luck!
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