A heavy-duty truck with a 24 V electrical system fails to start. When the technician attempts to crank the engine, only a single click is heard from the starter solenoid, and the engine does not turn over. A multimeter measurement across the battery terminals shows 24.5 V before cranking and drops to 8 V during the click. What is the most likely cause of this symptom?

Question: A heavy-duty truck with a 24 V electrical system fails to start. When the technician attempts to crank the engine, only a single click is heard from the starter solenoid, and the engine does not turn over. A multimeter measurement across the battery terminals shows 24.5 V before cranking and drops to 8 V during the click. What is the most likely cause of this symptom?

Answer options: ✅ Severely discharged or faulty batteries

• A short circuit in the starter motor armature
• An open circuit in the starter motor field windings
• Excessive resistance in the starter solenoid coil

Correct answer: Severely discharged or faulty batteries

Explanation: A significant voltage drop to 8 V across the battery terminals during an attempted crank indicates that the batteries are unable to supply the required current, which is characteristic of severely discharged or faulty batteries. A short in the starter motor armature would likely cause the voltage to drop due to excessive current draw but the battery itself would heat up rapidly or the cables would glow. An open circuit in the field windings would prevent the starter from turning at all, with less current draw and thus less voltage drop. Excessive resistance in the solenoid coil would typically result in a weak magnetic field and potentially just a click without a significant drop in battery voltage if the main starter circuit doesn't close.