An indication of alternator output can be obtained by

• A. Comparing battery voltage with engine off and engine running
• B. Measuring oil pressure
• C. Checking coolant temperature
• D. Reading tachometer

Answer: (A)

This tests how the charging system shows its output by looking at the battery voltage with the engine off and with the engine running. When the engine is off, a healthy battery voltage is around 12.6 volts. Once the engine is running, the alternator should raise the system voltage to about 13.8 to 14.4 volts as it charges the battery. Seeing this voltage rise indicates the alternator is producing electrical power for the system. If the voltage doesn’t rise, or stays too low, there may be an issue with the alternator, belt, or voltage regulator. The other indicators—oil pressure, coolant temperature, and tachometer—relate to lubrication, cooling, or engine speed, and don’t directly reveal how much electrical output the alternator is generating.