The John Deere L100 lawnmower runs a 12-volt system; the battery on any machinery needs a voltage regulator to keep the battery charged. When the lawnmower is running, the battery runs all the electrical components and the voltage rectifier sends 14-volts back to the battery to keep the lawnmower operating. Checking the voltage regulator requires knowledge of how to use a multimeter. This procedure will take 10 minutes to complete.
Park the lawnmower on a hard, level surface and set the parking brake. Turn the key in the ignition to the "off" position.
Open the bonnet of the mower and locate the voltage regulator on the left side of the engine bolted to the engine shroud. Disconnect the wiring harness from the bottom of the voltage regulator.
Set the multimeter to the ohms scale. Attach the black lead to a ground on the engine. There a three prongs coming from the bottom of the voltage regulator; place the red lead from the multimeter to the prong furthest from the operator's seat. The reading on the multimeter should be 31.2m. Leaving the black lead on the ground, place the red lead to the middle prong. The reading should read 8 to 9m on the multimeter. Place the red lead to the last prong, leaving the black lead to ground; once again the reading from the multimeter should be 8 to 9m.
Replace the voltage regulator if any of the reading is not within the specifications.