With power to the bus and the fuel selector switched to the right-hand tank, how many relays in the system are operating?

• A. Two.
• B. Four.
• C. Three.
• D. Five.

Answer: (C)

When power is on the bus, the fuel system’s control path is ready to operate. Selecting the right-hand tank completes the signal path to that tank’s fuel pump. This energizes a chain of relays: the main fuel-pump supply relay (providing power from the bus to the fuel system), the right-tank pump relay (which actually switches power to the right-hand pump), and the selector/interlock path that enables the right-tank circuit. All three coils energize, so three relays are operating. If the selector changes or is removed, the interlock would stop energizing the others, reducing how many relays are active.