How to Test a Voltage Regulator on a Harley Davidson

We have been asked a lot regarding wheel spacers. Many riders have doubts about which spacer goes where when they have disassembled their wheels.

You can find which one(s) you need in the following Harley Davidson wheel spacer chart:


What Are the Components of a Bike’s Charging System?

When your bike isn’t functioning properly, there’s a high chance that there’s something wrong with its charging system. It’s important to understand which part is faulty before you attempt any repairs.

Here are the 5 main components that form a bike’s charging system.

  • Voltage regulator
  • Battery
  • Alternator
  • Cables
  • Switches and fuses

In this article, let’s focus on dealing with the voltage regulator.



What Is the Function of a Voltage Regulator?

When your motorcycle is in motion, the voltage regulator plays a crucial role in managing the electrical current generated by the alternator. Its primary function is to convert the alternating current (AC) produced by the alternator into Direct Current (DC), which in turn charges your motorcycle’s battery. Any surplus current that exceeds the battery’s requirements is efficiently transformed into heat by the regulator.
The rapid heating of voltage regulators can be attributed to this conversion process. The continuous temperature fluctuations place considerable strain on the regulator, contributing to its endurance over time. Typically, motorcycle regulators tend to exhibit signs of malfunction after the vehicle has traveled approximately 31,000 miles.

How Do I Know My Voltage Regulator Isn’t Working?


Understanding the role of the regulator reveals its susceptibility to overheating. As it tirelessly converts current from the alternator into Direct Current for the battery, the regulator becomes vulnerable to frying. It is important to note that the excess current is converted into heat, and an excessive amount of heat can lead to the malfunctioning of this component.


Optimizing bike battery performance is crucial for ensuring smooth operations. Ideally, a bike battery operates optimally when supplied with a voltage ranging between 12 and 14.5 volts. However, if the voltage regulator fails to convert the alternator’s output correctly, it may result in an overvoltage situation, where the battery receives close to 20 volts of power. This excessive power can lead to the premature depletion of the battery’s charge. It is worth noting that bike batteries should be replaced every five years to prevent potential issues. After this timeframe, there is a possibility that the voltage regulator could be damaged, further emphasizing the importance of regular battery maintenance.


What if you examined your bicycle and discovered no apparent problems with your voltage regulator and battery? It’s possible that your charging system has loose wires. When encountering bumps or potholes, it is common for wires in the charging system to become loose or dislodged. The consistent jarring can lead to damage in the connections between the regulator and battery.

Make sure the necessary wires are secured before and after you ride your Harley.

Tools You Need to Test the Voltage Regulator

There are a few tools that you require to test and change your regulator.

  • A multimeter
  • A ⅜ inch socket wrench
  • Needle-nose pliers
  • An Allen wrench
  • Gloves

Testing the Voltage Regulator on a Harley Davidson


Before you begin conducting tests on your regulator, it is crucial to ensure that the battery of your bicycle is fully charged. Failing to do so may result in inaccurate readings from the multimeter. To charge the battery, you will need to remove the seat from your bicycle.



After charging your battery, you can now test the voltage from the regulator. Take your multimeter and test your voltage with the bike engine turned off.

What does the multimeter reading mean?

  • If the reading from the multimer is above or at 12.4 volts, then you have nothing to worry about.
  • If the voltage is less than 12.4 volts, then you may need a new battery.

Is your Harley brand new? Have you changed the battery within the past few weeks? In either case, you need to double-check why your battery died out this fast.





Now, do the same test with the bike engine turned on. Let the bike heat for a bit before checking the voltage.

  • When your bike is idling, the reading on the multimeter should be between 12 and 13 volts.
  • Once you hit the throttle, the reading should not exceed 15 volts.

If the voltage does not reach 12-13 volts, then you probably have a faulty regulator. However, you need to check and change your regulator if the reading exceeds 15 volts when the bike is revved up.

Changing the Voltage Regulator on Your Harley Davidson

If the voltage regulator on your motorcycle does not align with the optimal settings, it is recommended to replace the component. Thankfully, there is no necessity to visit a mechanic for this straightforward procedure. This comprehensive guide will assist you in swiftly and effortlessly replacing the voltage regulator, ensuring smooth functioning of your bike.


To begin, the initial step involves disconnecting the outdated regulator. The placement of regulators varies depending on the specific model of the motorcycle. If you’re unsure about locating this component on your Harley, refer to the service manual for guidance.

Upon identifying the regulator, you’ll observe that it’s secured using two ⅜ bolts – one positioned at the top and the other at the bottom. Utilize a ⅜ inch socket wrench to detach each of these bolts. The process of removing the bolts should be relatively effortless. It’s crucial to store the voltage regulator bolts in a secure location as you will require them later on.



After removing the bolts, you must unfasten the two wires that are attached to your alternator. These are usually under the regulator. If you can’t find the wires, refer to the service manual of your Harley Davidson.

  1. Once you spot the wires, remove the zip ties that hold them together. There should be two of them, one tied at the top and one at the bottom. After removing the zip ties, you can safely disconnect each wire.
  2. One of the attached wires is trickier to remove than the other. You can identify this connection because it has a little button that you have to press to loosen it.
  3. Press that button and use your hands to jiggle the wire out of its socket. Don’t apply too much pressure as you don’t want to get any nicks or scratches on the wire.
  4. To unplug the other wire, simply remove the wire from its socket. There aren’t any buttons you need to press on this one.
  5. After detaching both wires from the alternator, you can now remove the regulator from your Harley.


  1. After taking the old regulator out, don’t place the new one just yet. Take a cloth and clean that area thoroughly. You don’t want any dust or grime in that area.
  2. Once that’s done, you can place the new voltage regulator in its frame. Replace the wires the same way they were before you removed them. If you’ve forgotten or don’t remember how they were placed, refer to your service manual.
  3. Remember, the regulator goes in at an angle. Keep adjusting the position a few times till you see the regulator sit perfectly in its place.
  4. Now, take the ⅜ inch bolts you removed earlier and tighten them on your new regulator with a socket wrench.
  5. Ensure you clean the old bolts as well. Carefully remove any accumulated dirt or dust.


After reattaching the regulator, make sure to connect both wires to the alternator. It is crucial to insert each wire into its designated socket to ensure proper functioning of the voltage regulator. Remember the wire that was difficult to remove? Well, reattaching it requires the same level of delicacy. Begin by securely placing the wire into its snap. Then, verify that it is centered and well-balanced. Finally, gently insert the wire into its socket until you hear a satisfying click.

Once both wires are securely attached, you have successfully replaced your regulator.




You’re almost finished with the entire procedure. Once you’ve replaced your regulator and reconnected the wires, it’s crucial to secure the cables tightly to maintain their position. For this purpose, you can utilize zip ties just as before.
Remember that you removed two zip ties earlier, one at the top and one at the bottom. The specific placement is not significant as long as the wires are securely fastened. Once you have tightened the wires using zip ties, you can trim off the excess ends.


Once you have replaced the old regulator with the new one, it is essential to perform a voltage check using a multimeter. Follow the same steps as before to ensure accuracy. The voltage reading should now fall within the recommended range for your Harley motorcycle. Make sure to test the voltage while the bike is both idling and under acceleration.


Replacing and testing the voltage regulator on a Harley Davidson motorcycle is a straightforward process. Necessary tools can be easily obtained from local hardware or motorcycle supply stores. Instead of relying on costly services provided by mechanics or Harley repair shops, which could result in unnecessary expenses, it is highly recommended to undertake this task on your own. By personally changing the voltage regulator, you can complete the job within a maximum of 10-15 minutes, saving a significant amount of money. Therefore, opting for a DIY approach to replace the voltage regulator on your Harley Davidson is the most efficient and cost-effective choice.

How to Test a Voltage Regulator on a Harley Davidson
How to Test a Voltage Regulator on a Harley Davidson