Why not use the setup that the factory designed, with an oil pressure operated switch? A fused wire from any convenient 12V source, such as the battery cable connection at the starter is run to one side of a normally-open switch that's closed when the engine starts by oil pressure. The other side of the switch feeds the choke(s). If the engine stalls, the chokes quit heating, so a restart isn't a problem. All the factory electric-heated chokes use somer sort of interrupter circuit in case a cold engine stalls. It's also idiot-proof, so you don't forget to turn the heater on when it's needed.
Jerry
