Voltage regulators keep the power generated by alternators consistent to prevent damage to the battery or other components in the vehicle's electrical system. On older vehicles this device is usually separate of the alternator, whereas on newer model vehicles the voltage regulator is more likely to be built into the alternator. Some cars and trucks may even use the ECU to maintain proper voltage.
There can be a variety of issues experienced when a voltage regulator fails. The vehicle's lights could pulse, the battery could die or show low voltage, and the engine can even run improperly (stalling, low power, missing).
Where the voltage regulator is, and whether or not it can be replaced separate of the alternator, will vary greatly depending on the application. Consult with a professional automotive technician or repair manual for more information.
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