[76FJ55]

Originally Posted by wazzz

It is actually the other way around. When ignition is on, but before cranking, relay coil is energized as it receives power (+12V) on 86 from Ignition On (bus 15) and ground on 85 through the sensor plate switch, which is closed because engine is not running yet. Since coil is energized, SPDT relay switch has toggled and closes circuit between 87 (bus 50) and 30 (fuel pump positive side, not to be confused with permanent power bus 30).
So when cranking, power is applied on bus 50 (yellow wire) and goes to FP through 87-30. FP is then powered and running. As soon as engine begins to turn, airflow lifts the plate and sensor switch opens, hence the relay coil no longer receives a ground and is no longer energized. Relay switch toggles back to rest position 87a-30, which takes on to provide power to FP from bus 15.

Safety feature: in case of accident, if ignition is still on (driver unconscious), provided the engine has stalled, sensor plate switch closes again, so ground is provided to relay coil, which is therefore energized again, and relay switch toggles to 87-30, but since there is no power on 87 from yellow wire, terminal 30 has no power. Therefore FP is no longer powered and running.

I'm not sure you diagram with the diode can emulate this behavior.

Thanks for the clarification. I was thinking along the lines of L-Jet not K-Jet, and misinterpreted the airflow contact sensor contact. I should have know since 87a is the normally closed contact and 87 is the switched contact. You're probably right that the initial proposed diode I proposed. I'll have to think about it and see if I can come up with a viable solution with this new information.