A power supply to keep the voltage consistent is required. This video is sponsored by Auto Value and Bumper to Bumper.
Voltage drop testing compares the battery or charging voltage to the voltage at the component.
The measurement of voltage is like the speed of highway traffic – when loads are light, the voltage does not drop.
Andrew Markel shows how to voltage drop test a starter when there is a slow crank, despite the battery and starter having enough voltage. Sponsored by Bosch Automotive Service Solutions.
Most alternators fail electronically long before they wear out mechanically. Even so, the shaft bushings and brushes are wear items that don’t last forever. These parts can be ruined if the alternator is mounted low on the engine and is subjected to road splash that contains salt water or debris.
If the charging voltage is low, or the alternator isn’t putting out enough current to keep up with the electrical loads that are placed upon it, don’t automatically assume the starter or alternator is bad and needs to be replaced (unless you’re bench testing the unit out of the vehicle). Many times an alternator is