Here's another method, which is what the manufacturers do with electric-heated chokes: Use a switch activated by oil pressure. If the engine stalls during warm-up, the choke heater disconnects. It's also a positive way to be sure the heater only works when the engine's running. Tap into the oil gallery where your oil pressure line connects, and use the switch that's found just above the oil filter on a late-model V-8. There are 3 terminals, one which grounds the idiot light, and a normally-open set of contacts. Connect one to a fused lead connected to battery or ignition voltage, and the output lead to the hot wire on the choke. The choke heater works only when there's oil pressure present.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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