Voltage measured across a turn signal bulb should be:

• A. full source voltage
• B. zero volts
• C. half of source voltage
• D. variable depending on load

Answer: (A)

When a turn signal is active, the bulb is connected directly across the battery through the flasher switch. The circuit path is a single load with only small drops from wiring and contacts, so almost all of the supply voltage appears across the bulb. In other words, the bulb sees the full source voltage, which is why it lights up brightly.

If the voltage across the bulb were zero, the circuit would be open or the bulb would be off. A half voltage would require a deliberate voltage divider in series with the bulb, which isn’t how a typical turn-signal circuit is wired. The source is designed to provide near-constant voltage to the lamp when it’s on, with only minor fluctuations from wiring resistance or battery condition.