Electrical System: Voltmeter

The DC voltmeter is used to measure circuit voltage. A voltmeter with a range of 15 V or more is used by connecting the positive (+) probe (red lead wire) to the point where voltage will be measured and the negative (-) probe (black lead wire) to a body ground.

Fig 1: Measuring Procedure Of Circuit Voltage By Using Voltmeter
Courtesy of MAZDA MOTORS CORP.