How to perform a Voltage drop test

This test checks for voltage being lost along a wire, or through a connection or switch. (see diagram below)

1. Connect the positive lead of a Digital Voltmeter (DVM) to the end of the wire (or to one side of the connection or switch) which is closer to the Battery.
2. Connect the negative lead to the other end of the wire (or the other side of the connection or switch).
3. Operate the circuit.
4. The Digital Voltmeter will show the difference in voltage between the two points.

Typical voltage drop maximums:

• Battery post to battery terminal = 0 volts
• Main (-) cable to engine block = 0.20 volts
• Engine to body (-) Ground strap = 0.20 volts
• Battery (+) main cable (end to end) 0.20 volts (This main connect to the starter or Buss, depending on year, make and model)
• Battery post (+) to alternator battery (+) bolt = 0.5 volt with maximum charging load applied (all accessories on)
• Battery post (-) to alternator metal frame = 0.20 volt
• starter circuit (including starter solenoid) = 0.60 volts
• starter solenoid = 0.20 volts
• Battery Negative (-) Post to metal starter body = 0.30 volts

Voltage drop readings that exceed the above standards indicate a problem that needs further investigating.