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How to Replace a Starter Solenoid on a Lawn Mower

The starter solenoid on a lawn mower acts like an electronic switch. When the ignition key for the mower is turned to the "start" position, the solenoid engages and sends electrical current from the battery to the starter. When the solenoid fails, there is no way to repair it, and it must be replaced.

Place the mower on a level surface. Open the hood of the mower and remove the negative battery cable by unscrewing the the cable nut with your ratchet and the correct socket.

Trace the positive battery cable to the solenoid. The first place the positive battery cable connects to leading away from the battery is the solenoid.

Disconnect or unplug each wire connected to the solenoid. In some cases, they will just be wiring harness plugs that can be pulled apart. In other cases, connecting nuts on electrical posts must be loosened before the wires can be taken off. Mark each wire removed by wrapping a piece of masking tape around it, and using a pen, label the post it came off. For example, a wire removed from the upper left post can be labeled "TL" for "top left."

Unscrew the bolts that anchor the starter solenoid to the lawn mower chassis. Take out the old solenoid.

Bolt in the new solenoid exactly the way the old one came out. Attach the wires to their correct electrical posts as marked on the masking tape, reconnect the negative battery cable and close the hood.

Test A Mower Starter

It is the beginning of the mowing season and the grass is green and high, you climb on your trusty riding mower and turn the key and you here a slightly audible click but the riding mower doesn't start. the problem may lie in the mower engine starter motor. The battery charge reading on the voltmeter should be roughly 12.6 volts for a full battery charge. Check the battery terminals and battery cable ends for dirt and corrosion. Unscrew, using a socket wrench or combination wrench, the nut that holds the battery cable end to the large starter solenoid lug Clean corrosion and dirt from the battery cable end and large solenoid lug with a wire brush. Inspect and clean the smaller remaining lugs on the engine starter solenoid. Mower engine starter solenoids generally have three or four lugs: two large and one small or two large and two small. Engine starter solenoids with three lugs use the solenoid mounting ears as a ground, having only one small lug that connects the starter switch wire to the solenoid. If the starter motor does not turn over or run, then the engine starter motor is faulty and requires replacement.

Tip

To keep hands free of nicks and cuts from sharp areas under the mower hood, wear a pair of light-duty gardening gloves.

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