OK great news so far then.
Friction fit connections might come loose, but you'll know what to do to fix it. I've had a further look and found some original instructions which clarify a few things.
Looking at the car's horn and indicators / hazard light control circuit most of it is quite buried without removing further bits of trim, but the rear indicator lights cabling runs down the drivers side of the car and can be traced from the footwell. The indicators take quite a lot of power (21w + 5w + 21w) x 2 = 94w so it's seems beneficial that the two brown wires from the kit are fairly thick. You can connect one brown wire to the left hand indicators and the other brown wire to the right hand indicators, but they will need to be good connections to support the potential current draw.
The circuit diagram shows green/yellow for RH indicators and green/red for LH indicators, you could trace back the cable bundle that runs along the drivers sill to find where the connections are made to the under dash fusebox. (It's also a junction box with connections on both sides).
I'm not certain what the siren/horn connection will achieve, bibbing the horn when locking or unlocking is not much use. If it's for a panic alarm that might be worth it. You can hear the locks operate from quite a distance so that's all you really need to be sure it's working.
The horn is driven by a relay so you ought to use that rather than connecting directly.
The circuit diagram shows it's the orange wire routed from the steering column to the engine bay fusebox. There will be a junction between the dashboard loom and the engine bay loom again in the under dash fusebox area.
Beware of just finding the correct colour wire somewhere, as the same colours get used in different places for different things. For instance the green/red used for the LH indicators is the same colour as an electrical load sensor wire from the engine bay that also goes via the under dash box en-route to the car's main computer. Easiest method is to isolate and tape up the spare wires, then it will be the same as cars with factory remote, they don't have sirens or flash the indicators.
Remember to disconnect battery when making changes to the wiring, it only takes 12v in the wrong place to fire an airbag or seat belt tensioner.
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TG
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