I've noticed that there is a short delay (half a sec) before the horn sounds for the first time - after that it's instantaneous. So I imagine that the horn has a capacitor which dissipates once the ignition is off.

Do you think it would be a good idea to wire in a capacitor before the switch? Or is there a better way of doing this?

Thanks in advance

I don't think a capacitor will make any difference (but I could be wrong) plus it would discharge after a day or so. I've got a Klaxon on my TL and had to wire a separate switch and 30amp relay from the battery as when I tried using the original factory wiring I had too much voltage drop and the horn sounded sad.