I understand what you mean about not removing the tire. If you install the horn and did not jack up the car or remove the tire, hats off to you. I don't see how anyone could do that without damaging the wheel lining material.
I had to jack up my car, that causes the wheel to sag down and give me just enough space to remove the wheel lining material.
I will not get it activated because I called 2 dealers ($120 and $109) to activated it. I said no. So I paid $230 for a blinking lights