I pre-wired the horns but left extra length. Then I removed the front end of the car, used self tapping screws into the bumper support to mount them and also double as a grounding point, wired them together and cut the wire to the right length, unplugged the stock horn, and plugged in the wire from the new horns with a terminal on the end. It was a pretty easy job but time consuming to get everything how I wanted it to be.
They are pretty awesome though. People get scared when they try to merge into me or cut me off. I see them swerve when I lay on the horn.