The choke applies itself with a bimetal spring anytime the temperature cools down. No electric input is necessary for that to happen. The electric part comes in for releasing the choke, usually within one minute of run time in warm weather or a max of 3 minutes in sub-freezing temps. If the engine stalls with ignition or accessory voltage applied to the choke, it continues to heat and release, and makes a restart difficult. I like to run the choke release voltage through an oil pressure sensing switch, so the choke heating only happens while the engine is actually running and the switch has oil pressure applied to it.

Try using a 3-terminal oil pressure switch from a mid-1970's Chevy Vega tapped into the same oil gallery that supplies the oil pressure gauge. Connect the voltage from the fuse block you pictured to one of the normally-open terminals, with the other N.O. terminal connected to the choke. A 10 amp fuse should be plenty to operate the choke heater. Oil pressure will close those contacts and heat the choke coil while the engine is running. Either leave the normally-closed contact with nothing connected to it, or use it to ground an idiot light to supplement your oil pressure gauge.
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!