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?

Wire is normally sized by the current rating to avoid overheating of the wire.

Here that is not a problem as the horn is only on for a few seconds occasionally. So the wire has to be sized by its volt drop over the total circuit length. Just a similar cable to the one on the existing horn should be a good choice. The rest of the fixed wiring and the relay will see twice the current but should not be a problem.

For reference on some cars the relay is permanently powered and operated by grounding the other relay coil pin through the horn push button. Some do this through electronics from the horn push button.

My conclusion is just put the second horn in parallel with the original horn using a similar size wire. The fixed wiring is probably already sized for two horns as used on other varients such as in my Elegance model.

Thanks, that's what I've always reasoned in the past to get rid of the beep-beep horns. Even mains plug fuses won't blow at their rated current unless they get it for about 30mins.

Just seen the wiring diagram and noticed that the horns are solidly grounded and have a switched supply. They probably have seperate grounds so that at least one horn will still work if a ground connection is corroded. You can still just wire the new one across the original, if you have one with the right note.

You could also do as you have done before and just replace the the single horn with a twin pair using the single horn wiring. The wiring from the relay is only 1mm squared and that is for two horns so Skoda are happy with the volt drop in the cable.