Oddly the Mazda came with no horns – I guess a previous owner must have harvested them for something else. When I pressed the button I could relay trigger so that looked good. An online manual confirmed the green/yellow wires where for dual horns. Luckily I did have a set of horns from my old Hyundai Stellar kicking around. They weren’t the self grounding ones like what the Mazda probably had but I added a ground wire to each. I even had a spare bolt in the bolt bucket so a zero dollar repair.
The red primer is showing through in places so one day I’ll have to try and match the yellow and respray in the engine bay.
My starter is pulled and the new one should arrive today along with the brakes parts.