Final answer:
To test for ripple voltage from an alternator, select the AC voltage mode on a digital multimeter and connect the leads to the alternator's positive and negative terminals. A high ripple voltage can indicate alternator issues.
Step-by-step explanation:
To check for ripple voltage from the alternator using a digital multimeter, you need to select the AC voltage mode (often denoted as 'VAC' or 'ACV' on the multimeter) because the ripple is an AC component superimposed on the DC output of the alternator. When testing for ripple voltage, connect the positive lead of the multimeter to the positive terminal of the alternator's output, and the negative lead to the ground or negative terminal. A high reading in AC voltage mode could indicate a problem with the alternator's diodes or a faulty voltage regulator. Remember to set the multimeter to the correct range that can measure the small AC voltage of the ripple over the DC, which is usually within a few hundred millivolts.