The voltage regulator on a John Deere lawn mower is responsible for ensuring a smooth, consistent charge back to the machine's battery. Lawn mowers run a 12-volt system to keep the battery charged. The stator on top of the engine must create 14-volts to send back to the battery. As the 14-volts is sent back, it must first go through the voltage regulator, where it evens the voltage current, so no damage is done to the battery or the electrical system. This procedure requires knowledge on using a voltmeter.
Park the lawn mower on a hard, level surface. Set the parking brake and turn the ignition key to the "off" position.
Move the foot pedal back to the "Neutral" position. Raise the hood of the tractor and turn the ignition key one position over to turn on the mower's headlights without turning over the engine for 15 seconds to place a small load on the battery.
Turn on the voltmeter and set it to 50 DC scale. Place the positive (red) lead from the voltmeter to the positive (+) battery terminal; place the negative (-) lead from the voltmeter to the negative battery terminal.
Start the engine and advance the throttle to the FAST position. Read the voltmeter over a period of five minutes of run time, voltage should remain between 12.2 volts and 14.7 volts DC.