I 've fitted twin horns on other cars in the past by just removing the single and connecting the new hi-lo pair to the original wire. I was young then. Now I'm more cautious, whats the practical thoughts on doing this on an Octavia Mk2? If I use 2.5mm2 wire I don't envisage a problem, but if I ask questions the recommendation is to fit another relay and add a fused power wire from the battery. That makes it a tedious job. Does any of the Mk2s have twin horns, and what size wire was used?

I'm guessing that's 1.0mm².

Well, it looks like they just added a second horn in parallel if you have posher trim. Not sure about the wiring thickness, as the main wire from the supply control unit appears to be 0.5, though it's a bit blurry when I zoom in. Strange diagram for the relay as it's control wire might be to pin 11, and so a ground operated line, but if the diagram is correct , that would ground the horn as well.

0.5mm². BR is the universal wire colour for earth.

The 11 in the box is to fuse 17 in the E Box. Which would be the engine compartment fuse box. The other end of the fuse is connected to the car battery, so is a permanent live.

Many thanks, that makes more sense. So since Skoda just parallel the horns the AI suggestions of using 2.5mm ² is not fact based.

PS how do you get the correctly formatted superscripts for wire sizes?