What position should the engine control switch be in when starting a single unit generator using an auxiliary fuel source?

The correct approach to start a single unit generator using an auxiliary fuel source involves placing the engine control switch in the "Prime and run aux fuel position." This specific position allows the generator to utilize the auxiliary fuel system effectively, ensuring that fuel is properly supplied to the engine for ignition.

In the prime state, the auxiliary fuel system is activated, allowing fuel to reach the engine's combustion chambers before main engine operation begins. This is particularly important in scenarios where the primary fuel source may not be sufficient for starting the engine or when the generator has not been used for an extended period.

Once the necessary fuel is primed, the engine can then transition to the run phase, allowing it to operate normally on auxiliary fuel. This sequence is designed to prevent starting failures and ensure reliability in fuel supply, which is crucial for generators that may rely on multiple fuel sources for operation.

Other positions would not provide the engine with the necessary setup for starting with auxiliary fuel, making the "Prime and run aux fuel position" the most suitable choice for this situation.