None that I can think of. My old GS has twin horns with no relay. Usual current and voltage checks obviously.
Have you tricked around with the adjuster screw ? The old horn may have life in it yet.
Generally hidden under a blob of sealer. The internal contacts wear and a bit of adjustment can revive a dead unit or improve the sound of one that's going off.
In all my years riding I have never used the horn(s). Generaly the times you might want to someone is doing something incredibly stupid or is blind or both. If I thought that a horn blast could improve eyesight or concentration I would push the button but there is no way of knowing what the reaction will be to loud noises so as usual I just learn to be the invisible man.
Anyway the time to push the button could be a whole second that could be better spent organising the anchors and looking for the bolthole.