I did the swap using PIAA sports horns a few weeks ago... I bought the same horns I bought previously for a Nissan Patherfinder, but later moved to split between a Honda Fit and Honda Ruckus. Sure, I could've taken the horns off the Fit and Ruckus... but I still intend to use the Fit and Ruckus, plus I cut the splash "shield" from the horn when I installed it on the Ruckus.
It came with ground wires which were quite lengthy, so I just twirled it around the back where the bracket mounts. I also ordered some adapter wires from Amazon... you can find the same thing from College Hills Honda (both adapter plus ground wires)...
The driver side was a bit of narrow reach, but easier than the passenger side. I took out one pin and one screw along the fender, then two more pins holding the fender to the underside. At that point, I pulled the fender away and reached in through there. Now that was a tight squeeze since I didn't jack it up and only turned the front wheels to the other side... and annoying as hell trying to ratchet the old one out and then new one in.
I guess my time blindly doing PC parts repair influenced this... I mean literally, there are times I had to plug in things in the PC where I couldn't see a thing and had to rely on "this thing feels about right." >.<
I'm sure that your PIAA horns are way better than the used Accord horns I used but US$3.75 is my preferred price range!
The drivers side horn is easy to swap. For the passenger side, I accessed it from underneath.
3 push pins, pulled the plastic flap down and it was easy.
As I mentioned, these push pins were unique and all 3 broke which I had to replace.
These minor upgrades are trivial, but once you start addressing all the weak points of a vehicle, it becomes a much better overall vehicle.
Some call it getting the "cheapness" out of a vehicle.