It's best to power electric choke(s) from an oil pressure switch. Simply connecting to a switched voltage source is OK as long as the engine doesn't stall during warmup. If that happens, the choke heaters continue to operate and the choke releases, making the engine hard to restart. A combination idiot light/fuel pump switch for a Chevy Vega, or any other GM product with an electric fuel pump makes a good addition to the circuit. Any 12V source can be used to supply power to the pressure switch.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!