Final answer:
A second fuel pump alarm most likely indicates an Electrical malfunction since primary alarms typically detect mechanical issues, and electrical issues can trigger subsequent alarms.
Step-by-step explanation:
When a secondary fuel pump alarm activates, diagnosing the exact issue requires consideration of various potential causes. However, if we are looking at the most probable reason, option B, Electrical malfunction, is a likely culprit when a secondary alarm triggers. This is because primary alarms often detect mechanical or performance issues such as low fuel pressure, which would likely have tripped the first alarm. Electrical malfunctions can range from a blown fuse, faulty wiring, or a bad electrical connection, and might not affect the pump operation immediately, thereby tripping a secondary alarm.
Among the given options, overheating or fuel contamination could initially trigger more specific warning systems before affecting the fuel pump operation to the extent of setting off a secondary alarm. Therefore, the correct answer to what a second fuel pump alarm most likely indicates is probably B, Electrical malfunction.