Only one wire had to be ran- the positive wire from the Hunter thermostat. I used 22 gauge solid (phone) wire that's pretty stiff so that made it easy . The small relay went right in the breaker box as shown so 12 volt DC ground for the coil was handy and one side of the contacts was the existing positive from the AC breaker,the other side of the contacts that went to the breaker was 4 inches long so the whole thing was quite easy.
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This is a blow up off the wiring diagram on the side of the relay.
It has two sets of NO contacts (normally open) that close when the coil picks up so there are spares :)