How To Test A Voltage Regulator On A Riding Lawnmower (Do This!)

Typically, when it comes to lawnmower maintenance, owners have to worry the most about dull blades, old oil, and faulty spark plugs. However, because a lawnmower engine requires electricity to keep running, one other component could need replacing – the voltage regulator.

This piece is similar to an alternator on a car – it feeds electricity back into the battery so that it will stay charged for next time. So, if the voltage regulator is bad, the battery could drain more easily, meaning that you have to jumpstart your mower every time you use it.

To test a voltage regulator, you will need a multimeter and some work gloves. Simply connect the multimeter to the regulator’s output to see if there is more energy going into the battery than coming out. If not, then you will have to replace this component.

Overall, this project is relatively simple if you’re familiar with how electrical systems work. We’ll break down the various steps involved and illustrate how this system operates.

What You’ll Need to Test a Voltage Regulator on a Lawnmower

How To Test A Voltage Regulator On A Riding Lawnmower

1)Position the Mower

You will need to access the section underneath the flywheel to reach the voltage regulator. If you’re unsure whether the battery is the problem or the regulator, you will also need to locate the battery. We suggest working in your garage or under some kind of cover, as this job can take a little while, and you need to be able to see the readouts on the multimeter.

Make sure the lawnmower is cool before working. You will also have to start the machine several times during this process, so be aware of any fumes that could accumulate in closed spaces.

2)Locate the Voltage Regulator

This component sits below the flywheel on most lawnmowers since that is what generates electricity to feed to the battery. If necessary, check your owner’s manual to see where the regulator is.

When you see the regulator, you’ll notice two wires – one set going into the part and one going out to the battery. Typically, the input wires are yellow, and the output wire is red.

3)Test the Input Wiring

In some cases, the wires themselves may be damaged or faulty, which means that you have to replace them instead of the voltage regulator. It’s crucial to check each component to be sure your lawnmower will stop having this problem.

First, Disconnect the input wire (yellow) coming from the flywheel. Start the mower and then connect the positive and negative terminals from the multimeter (in that order). Your multimeter should be set to A/C power, as that is what is coming from the engine. In most lawnmowers, the electrical output should be over 20 volts.

Shut off the mower once you’re done testing.

4)Test the Output Wiring

If the yellow wire is working, the next step is to test the power coming from the regulator. Reconnect the yellow wires to the regulator and disconnect the output (red) wire. Start the mower again and connect the positive terminal to the wire. Switch the multimeter to D/C power.

Since there aren’t two elements to create a full circuit, you will have to touch the negative terminal to a metal piece on the lawnmower’s chassis. We recommend using tape to hold it there while you’re testing. Because lawnmower batteries are 12 volts, the output should be higher than that, at around 15 or 16 volts. If not, you know that the regulator is bad. Shut off the mower once you get an accurate reading.

5)Test the Battery Wire

If the regulator output seems normal, the next step is to verify that the wire to the battery is working correctly. Connect the positive terminal to the other end of the output wire (the side going to the battery) and then re-tape the negative terminal to the mower’s chassis. You should be reading 12 volts, even though the mower is off.

If you’re not reading anything, that means the wire itself needs to be replaced. Since it runs through the engine, we recommend going to a repair shop to get this done so that you don’t wind up making a mistake.

Bonus: Test the Circuit

If you have a jumper adapter for your multimeter, you can test the whole circuit to see if it is working properly. To do this, you will need to reconnect the input wires and output wires, but place a metal rod between the two sides of the red wire.

Start the mower, and then connect your jumper to the metal rod. It should show how much voltage is running through the circuit. If the number is around 12 volts, you know that the regulator is not working since no extra electricity is coming from the flywheel.

The reason to do this test last is to ensure that each component is working correctly (or incorrectly). If you did this step first, it would be impossible to know which part is faulty.

How a Lawnmower Electrical System Works

When working on any electrical components, it helps to understand how each piece works in tandem with the others. Here is a brief overview of how your lawnmower uses electricity to start and stay running.

Battery – Your mower’s battery is necessary to generate enough power to get the engine to turn over. Once the motor is running, the battery doesn’t have to do anything to keep it going. The battery is also a power source if you want to run any electrical elements when the machine is off.

Solenoid – Some riding lawnmowers come with a solenoid, which helps regulate the electrical current coming from the battery. Because there is such a burst of energy once the engine turns over, the solenoid protects the circuit from damage.

Flywheel – Inside the engine is a flywheel, which spins the crankshaft. To help it spin faster, there are magnets on both the wheel and the casing. As the wheel spins, it generates electricity from the magnets. This energy is what powers any electrical components on the mower, such as lights.

Voltage Regulator – The power coming out of the engine is an alternating current (A/C). The regulator converts that energy to a direct current (D/C) and sends it to the battery. Without the regulator, the current would overload the system and damage the battery.

For the most part, the main component that breaks down in this system is the battery since it will stop holding a charge as efficiently over time. Typically, a solenoid and voltage regulator will last for the life of the mower, so you shouldn’t have to test it very often, if at all.

That being said, electrical parts can break down for various reasons, including lack of use. So, if your lawnmower has been sitting for years, some of these elements may have corroded and won’t work properly.

Safety Tips When Testing Your Voltage Regulator

Whenever working with electricity, you need to be sure that you’re practicing safe protocols. Here are some tips to prevent any unwanted accidents, injuries, or damage to various components.

Wear Gloves – Doing this can insulate your hands from any electrical current.
Check Your Multimeter Settings First – Make sure that you are on A/C or D/C current when applicable. Otherwise, the multimeter won’t give you an accurate readout.
Always Start With the Positive Terminal – This is true when changing your battery or testing the regulator. When disconnecting, always work in the opposite order (so negative first, then positive).
Double-Check Connections Before Starting the Mower – You want to avoid overloading the circuit or damaging any of the wires.

How to Replace Your Voltage Regulator

Fortunately, once you’ve located this component and disconnected the wires, all you have to do is remove the fasteners to pull it off of the engine. Make sure to replace it with an identical part so that it will convert the current correctly.