Place the multimeter's testing probes across the two terminals of the battery to test the voltage in the vehicle's engine. While the engine is running, expect a reading of roughly 14.0 to 14.4 volts.
Turn on the vehicle accessories and the lights, then test the voltage across the battery. The reading should drop to 3 volts. A deviation in the voltage readings in these two steps means there is problem with the voltage regulator.
Disconnect the battery's negative terminal cable before performing any further operations on the electrical components of the engine. This is a vital safety precaution for you and will help protect delicate parts of the vehicle's electrical system.
Carefully pull out the cables connecting the voltage regulator to the alternator. The connection of the cable to the alternator is through a port through which only the head of the cable from the regulator can fit.
Unscrew the voltage regulator from where it is mounted using a screw driver. Make sure you do not lose these screws as they can be difficult and expensive to replace.
Remove the faulty regulator and attach a new one in its place. Replace the screws on the regulators and tighten them using a screwdriver.
Carefully insert the head of the cable from the new regulator into its slot on the alternator.
Replace the negative terminal battery cable and start the vehicle to test.