Here's how they work. There is a bimetallic strip (2 dissimilar metals) coiled inside an electrically heated housing. the coiled strip is connected to the choke plate in the primary side of the carb. Energizing (electricity) the heating coil heats the bimetallic strip. The two metals have a different rate of expansion, so the strip uncoils, opening the choke.
There is a single (hot) power wire to the choke, switched by the ignition switch. The choke heater grounds at the carburetor. Continuous power to the coil keeps it open. some choke power wires go thru an oil pressure switch, that only energizes the choke when there is oil pressure..engine running. Keeps the choke from opening too early.
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