How to test a voltage regulator. On any car with an alternator you have a voltage regulator. And this voltage regulator is responsible for keeping the voltage on the vehicle from exceeding a limit. Usually this limit is thirteen point eight to fourteen point two volts. Which is enough voltage to allow for proper battery charging but not enough to burn out light bulbs or damage delicate computer circuits. The best way to test a voltage regulator is with a multi meter and what you do is you put your multi meter clamps directly on the battery terminals. Positive red to positive and black to negative and you set it to voltage. And with the car off you should have a little over twelve volts that's a healthy battery. And when the, once you are hooked up you want to start the vehicle and what you'll see is that at idle the voltage will increase. This means that the alternator is charging the battery. We are making about thirteen point eight, thirteen point nine volts. And so at this point what you want to do is you want to slowly start increasing the speed of the engine and once you hit between fifteen hundred and two thousand rpm the voltage would reach a point where it no longer increases. And what we are noticing is that it's maxing out right around thirteen point nine eight, nine seven or so which is well within that thirteen point eight to fourteen point two, so this voltage regulator seems to be working fine. If the voltage keeps climbing with the rpm up in the fifteen plus volt range then the voltage regulator is not doing it's job and it needs to be replaced. If the voltage is too low then the alternator is not charging properly and it needs to be rebuild or replaced. And lastly, if the voltage with the vehicle off is below twelve volts then the battery is most likely in need of being replaced.