Selection of wire gauge is typically a factor of the current being drawn through it. The current in the kill circuit is virtually nothing…..you could use extremely small wire with no adverse electrical side effect.

That said, larger wire will offer structural integrity that is needed. The wires get flexed a bit as the mag plate turns, and you need something big & strong enough to tolerate it all. Personally, I used 16AWG on mine & it works fine.

Whatever gauge you decide on, use stranded, not solid. It aids in flexibility / durability.