I recently did some work on my car, and my low horn tone is not working. I've swapped the horns and it is not the actually horn unit itself, as both work on the set of wiring for the H tone. The wire is not severed or broken, the contacts are clean. The fuse is fine. Could this be something caused by a relay? Or is there likely a bigger wiring problem?

They share the same relay, so I would think there's something with your wiring for the low tone horn.