don't know about an early 120Y or 1200 wiring loom

but on a late (March '77) 120Y aussie 120Y the wiper motor wires and anti deseling switch (yellow wire) are in a 1 metre lead closest to the firewall - closest to the two rectangular pugs under the dashboard

then the headlight relay is on a short lead nearby

the horn wires are near the plugs for the indcators and parklights/under bumper indicators

I think they are green - 120Y's have 2 horn wires as they have 2 horns