Final answer:
A voltmeter is the vehicle instrument that measures the voltage in a vehicle's electrical system. Voltmeters measure voltage, whereas ammeters measure current.
Step-by-step explanation:
A voltmeter is the vehicle instrument that measures the voltage in a vehicle's electrical system. It is used to measure the potential difference between two points in an electric circuit. Voltmeters are placed in parallel with the voltage source to receive full voltage. Voltmeters measure voltage, whereas ammeters measure current.