How to wire a lawnmower ignition switch, step by step


The ignition switch does not seem like an essential part of your lawnmower, but it can be a pain if it is not working correctly. It can mean your lawnmower does not start, or you can not turn it off when it is running. If the ignition switch is broken, you have to replace it. Sometimes this can mean that you can find a replacement part that is an exact replacement. It means you can remove the old ignition switch and put the new one in. But sometimes the exact replacement is costly, or you can not find one. In that case, you have to use an alternative one. But it means you have to wire it to your gas lawnmower correctly. Most people find it annoying and difficult to repair and work on the electrical systems, but following the basic approach, these tasks become the easiest.

How to wire a lawn mower ignition switch

  • Step 1: Obtain a circuit diagram
  • Step 2: Locate all components that need wiring
  • Step 3: Connect the switch to ground
  • Step 4: Connect the switch to the Solenoid
  • Step 5: Wire the magneto to the switch
  • Step 6: Provide voltage by connecting the battery
  • Step 7: Connect the accessories/ lights
  • Step 8: Screw the switch in place
  • Step 9: Check if all is working well
How to wire a lawnmower ignition switch, step by step 1

Working of the ignition switch and Diagnosing the problem:

The ignition switch rotates when the key is turned and on different angles serves as a connection for different circuits. This turns on the different functions at the right time. When the contact points present in the switch wear away, or the terminal breaks off, maybe the spring present for starting fails, the switch will need to be replaced. Most ignition switches have the following postitions:

  • Switch in “OFF” position: Contact between magneto and ground is established. This will cut off the power from the engine, and the lawnmower shuts down.
  • “RUN” position: This position connects the accessories, i.e., lights, etc., to the battery. Some lawnmowers have different indications instead of “RUN,” but they serve the same function on the ignition switch’s second step.
  • Start position: When the key is turned in the start position, mostly spring-loaded, Solenoid and battery connection are established. The Solenoid is further connected to the starter motor that will start the engine.

All components involved in these steps are:

  1. Battery: The source of 12 V that is used for the various electrical components. It acts as the primary power source to run the accessories such as light, fan, etc. and cranks up the starter mechanism to start the engine. The 12 V is stepped up to provide the high voltage for spark generation as well.
  2. Solenoid: An electromagnetic switch that establishes a connection between the battery and starting motor. As soon as the key’s signal is received, the magnet becomes active due to current flow. It creates contact between the motor and battery, and the motor becomes operative.
  3. Starter Motor: It is the motor that turns the flywheel of the engine. It allows the air and fuel to enter the chamber and is compressed until the spark occurs and the machine becomes operative. Till this moment, the starter motor keeps cranking the engine.
  4. Magneto: This is a high voltage passing coil that takes the ignition coil’s energy. It also shuts the engine off when needed.
  5. Ground: The connection responsible for a good potential difference resulting in proper working of these electrical systems.

Knowing the working of these components is not enough. Before getting to know the ignition switch’s rewiring switch, it is important to beware of whether the ignition switch is faulty or not.

The test is simple and requires the use of a digital multimeter. The continuity of all the terminals is checked one by one. If your digital multimeter has a continuity mode with a beep, use that. You can also use the resistive measurement mode of the multimeter. Use the smallest setting. When the switch is working fine, you should measure almost 0 ohms. If you measure more or even no connection, the ignition switch is bad. Based on the function as mentioned earlier of each connect, the test is carried out. Three basic steps will be part of this diagnosis.

  1. Part 1: Put the key to “OFF”; this allows the contact between magneto and ground. Using DMM, touch the ground terminal and Magneto terminal. A beep sound indicates the switch has passed test 1.
  2. Part 2: Put the key to the “RUN” position; this will be checked by connecting the probes of DMM to the battery and Light terminal. If a beep sound is heard, Test 2 is cleared.
  3. Part 3: Connect the DMM terminal using small alligator clips to the battery and solenoid terminal. Turn the key as you turn it to start the lawnmower. If a beep sound is produced, the ignition switch is working fine and has passed all tests. 

Now you have learned all the basics and essentials of electrical systems. This will enable you to properly diagnose and fix the issue you have with your ignition switch. We will now look at the step-by-step approach to solve the ignition switch puzzle’s wiring.

How to wire a lawn mower ignition switch: Step-by-step Guide

Equipment Required

While wiring the ignition switch, a very basic list of items is required. Some of these items are a must, while others are necessary if any unforeseen happening occurs.

  • Grip Pliers
  • Electric tape (insulation of open connections and damaged wires)
  • Wires (color-coded) (Extension of smaller wires to the needed area)
  • Screwdriver
  • Open-ended spanner set (smaller numbers)
  • Solder iron (for soldering the terminals or connection if required)
  • Extra clips and clamps (if a preinstalled connection breaks off)

• Step 1: Obtain a circuit diagram

A circuit diagram is a schematic that indicates the layout of all basic connections. The model of the used ignition switch and other components are also shown. Circuit diagrams can usually be found in the instruction manual. There is nothing to worry about if you have misplaced your manual. You can easily find out the relevant diagram by searching by the make and model of the lawnmower. When you have found the circuit diagram, you should be able to find:

  • Connections of the ignition switch to all related equipment like Solenoid, battery, and magneto coil
  • A schematic approach to locate the general position of all equipment is established
  • The electrical connection of the components is also indicated in the diagram

Using the diagram helps a lot but even if it is not available. Using the diagnosis section’s information, anyone can develop a good approach for fixing any circuit-related problems.

• Step 2: Locate all the components that need to be connected

  • Battery: Start by locating the battery. It is usually present under the seat or at least the most prominent element, even if present under the hood.
  • Solenoid: Follow the positive terminal wire. This will lead you up to the Solenoid. A double cylinder small component that has 3 or 4 connections on it.
  • Lights: Lights are always present on the front of the mower and easiest to locate. Often they also have a separate switch.
  • Magneto: The Magneto is generally present right next to the relay and fuse box.

• Step 3: Connect the switch to ground

Connect the terminal with the indication “G” to the ground by either connecting the wire to the mower’s body, the battery’s negative terminal, or the ground terminal of the Solenoid. If you are unsure if the connection is good, use the multimeter to check it.

• Step 4: Connect the switch to Solenoid

Locate the positive terminal of the Solenoid. It is usually the lower terminal with a plus sign. Using a wire with clips on both sides, connect the “S” terminal to the Solenoid’s positive.

• Step 5: Wire the magneto to the switch

The coil of magneto that has a single open terminal is wired to the “M” terminal of the ignition switch

• Step 6: Provide voltage by connecting the battery

The positive battery is connected to the terminal with the “B” mark on it.

• Step 7: Connect the accessories/ lights

The wires from the lights are attached as a single to the terminal, indicating “L” or “Y.” It depends on the ignition switch type.

• Step 8: Screw the switch in place

After the connections are double-checked, screw the switch in position using the nut/screws you removed earlier, and place the rubber or plastic cover over it.

• Step 9: Start to check

Give the mower a check start. If any problem occurs, check all fuse and connections.

Precautionary Measures

  • Safety Equipment: Use proper safety equipment and insulations
  • Earthing: Ground heavy voltage equipment properly
  • Safety Switches: Use fuse where necessary and do not override safety switches
  • Clean terminals: Use a wire brush and sandpaper to clear away any deposits on the terminals.
  • Continuity: Use a digital multimeter to check the continuity of the wires before installation. If one of the wires is broken or shows a strange result, replace it.

Related Questions

1. Can you bypass the ignition switch that is broken?

Yes, it is possible, but it is generally a more complex process, and it is better to seek professional help while doing so. You need to pick the battery and Solenoid wires and strike them together to start the mower.

2. Can you jumpstart a lawnmower with a broken ignition switch?

You can jumpstart a mower with a bad ignition switch if the switch is functional in the start position. Otherwise, there is no possibility.

3. Even with the new ignition switch, the mower will not start. Why?

You have changed the switch, but still, the mower would not start. There can be two situations.

One scenario is where you have made a wrong connection. This can be just an error. Maybe the marking is in a different language that is difficult to comprehend. Or maybe any loose wire of accessories or fuel solenoid is making contact with the lawnmower’s body, causing the earthing of the battery voltage. This will even cause a shortening of the battery’s life.

The second scenario is that any terminal of the main component, such as the battery, ground, Solenoid, or starter motor, is very corroded and does not finely pass current.

Final Remarks 

Ignition switches are not prone to malfunction, but they can always fail. If this happens, they may become unfunctional, and the lawnmower can not be started or can not be turned off. A proper approach to install a replacement of the equipment is necessary. To know the exact problem, you need to diagnose the issue first.  

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