What's the verdict on your horn, thinking of doing the same on my T6.1 campervan, the current one sounds pathetic to be honest. Where did you order it from?Ok... so I've just swapped the crap horn for a Stebel Nautilus... the 2021 multivan is different from the California to access the original horn turn the wheels full left undo 2 x T25 hex screws along with what looks like a flat button fold the wheel arch cover back and with a13 mm spanner remove horn off bracket.. cut wires and join to new horn along with relay.. here's a great YouTube vid on how to wire it
Watch "How to wire Stebel 11690019 Nautilus Compact Mini Air Horn Black How to Test Instructions motorcycle" on YouTube