How To Check And Replace A Lawnmower Kill Switch

How To Check And Replace A Lawnmower Kill Switch

One of my most watched lawnmower repair videos over on Youtube is how to replace a lawnmower kill switch. I did some research into why and I’ve found the most common reasons most people think the kill switch needs replacing.

How To Replace A Lawnmower Kill Switch

To replace a lawnmower kill switch you will need to

remove the kill switch cover and disconnect the ignition coil wire. Usually, you can unhook the killswitch from its’s housing near the lawnmower brake with a flathead screwdriver. You can replace the switch by pushing a new one in its place and re-connecting the ignition coil wire. On other types of lawnmower, you will find a micro switch instead of a kill switch. To Replace a microswitch kill switch you need to disconnect the ignition wires and undo the microswitch. Re-connect a new microswitch and make sure it clicks when you operate the safety lever.

  • Note. Before you do any work on a lawnmower be sure to remove the spark plug completely

What Does A Kill Switch Do On a Petrol Lawnmower?

A kill switch is a safety feature designed to work in conjunction with a lawnmower flywheel brake. When the switch

is connected it stops the ignition coil sending any current to the spark plug, this, of course, means the lawnmower won’t start.

In the UK a kill switch is fitted by law. This is so you can’t leave a lawnmower engine running while you are not near it. In short, you need to operate a safety lever on the lawnmower handle to disengage the kill switch and allow the lawnmower to get a spark.

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The same happens in reverse when you let go of the safety lever or dead mans handle the switch connects and cuts off the spark. This is how you stop the lawnmower engine running. Without a kill switch, the engine would keep running until it runs out of fuel! So if you have a lawnmower that starts and runs but won’t stop then check the kill switch!

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Where Is A Lawnmower Kill Switch Situated?

On most lawnmowers fitted with a kill switch, you will find it at the back of the flywheel towards the back of the lawnmower. It is usually hidden behind a small plastic cover. If your lawnmower doesn’t have a kill switch it may have a microswitch fitted instead. This is usually the case on Honda lawnmowers. To find the microswitch, remove the starter recoil cover and you should be able to see it.

  • Note make sure the microswitch clicks when you operate the safety lever or the lawnmower won’t start!

How To Check The Lawnmower Brake And Cable.

For the kill switch to operate correctly it needs to disconnect from the swing arm. The swing arm has a metal tab that touches against the kill switch. This arm should swing out of the way causing it to disconnect from the kill switch. If it is dirty be sure to clean the switch.

The swing arm is operated by a cable attached to the operator handle. Operate the cable using the lever and make sure the arm swings out of the way and there is a clear gap where the kill switch and swing arm disconnect. If the swing arm does not operate and move away from the kill switch then the lawnmower will not run.

What Does A Lawnmower Brake Do?

The lawnmower brake sits against the flywheel. It moves out of the way with the swing arm when you start the lawnmower. When the safety lever is released the brake automatically touches against the flywheel and stops the flywheel and of course the blades from turning. It is operated by the same cable as the swing arm and works against spring tension to connect with the flywheel and “Brake” the lawnmower.

How To Test The Kill Switch?

One simple way to test the kill switch is to check if you are getting a spark. Remove the spark plug from the lawnmower but keep it connected by the ignition lead.

Set the spark plug against something metal, pull the lawnmower over while operating the safety handle and check for spark. If you have spark this tells you the kill switch ignition coil and ignition coil wire are all working. This eliminates the need to replace a kill switch.

How Often Do Kill Switches Fail?

I have repaired hundreds if not thousands of lawnmowers for profit and I have only once had a kill switch fail. More commonly it is a microswitch and not a kill switch that fails. Usually, the microswitch fails if it doesn’t get activated correctly by the safety lever. However, if the kill switch is dirty it won’t work and if it doesn’t disconnect it won’t work. That is not really the kill switches fault though is it?

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Let’s talk about the ignition wire that connects to the kill switch and how To Replace The Kill Switch Wire.

How To Replace The Kill Switch Wire

The kill switch wire connects directly into the kill switch. If you haven’t replaced it before it just pushes in underneath a small metal tab. Just bend the tab down and pull the ignition coil wire out. The ignition coil wire that connects to the kill switch can easily get broken. I have seen this a number of times when the starter recoil traps and breaks the wire. You will, of course, need to disconnect the ignition coil wire from the ignition coil itself. Check out this article that shows how to do just that.

How To Replace The Ignition Coil On A Petrol Lawnmower


How To Replace A Lawnmower Kill Switch.

To replace a lawnmower kill switch remove the spark plug. Do this before every single repair. Next, ask someone to operate the safety lever to move the brake and swing arm out of the way from the kill switch.

Disconnect the ignition coil wire by bending down the small metal tab then pull the wire out. The wire may be hooked over the edge of the switch so just unhook it first.

Take a flathead screwdriver and prise the kill switch out of the housing. This can take a little patience as it’s not really designed to be replaced. Take the new kill switch and seat it securely, then reconnect the ignition wire and release the safety brake. Now you can re-fit the spark plug.

Kill Switch Wiring Diagram.

The kill switch wire runs from the kill switch all the way around the flywheel and round to the front of the lawnmower where the ignition coil is. It sometimes connects to the underside of the ignition coil so read the article above to help you remove it.

The Briggs And Stratton Classic engine has an ignition coil that connects to the wire underneath the coil. The newer style of Briggs and Stratton Engine such as the 500E and 450E connect from the side which is much better.

Is Your Kill Switch A Microswitch?

Most Honda Lawnmowers use a micro switch instead of a kill switch. I have picked up multiple Honda petrol lawnmowers from local auctions that wouldn’t start simply due to the microswitch being incorrectly operated by the safety cable.

If the microswitch doesn’t click when you operate the safety lever then you won’t get a spark! This happens a lot on Honda lawnmowers so be sure to look out for Honda lawnmowers at auction centres that don’t show any signs of starting at all. Honda lawnmowers have incredible re-sell value.

Replacing A Lawnmower Microswitch.

If the microswitch appears to be working incorrectly and you wish to replace it then unhook all the wires taking note of where they go, then remove the microswitch and replace it. A quick tip is to use some long nose pliers to disconnect the wires from the switch. Once again though check for spark before you decide to replace the switch. If you have spark then the microswitch is working correctly.

What’s Best A Kill Switch Or Microswitch?

It’s a case of plusses and minuses. I personally prefer a kill switch simply because its easier to access and also fails less frequently, if at all. Microswitches are often fitted to better quality lawnmowers though and can be a really simple fix if it’s just not connecting properly.

Here’s a video that shows where you will find a micro switch on a petrol lawnmower rather than a traditional kill switch

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Can I Remove/Bypass The Kill Switch?

In theory, yes you could as the lawnmower would start and run and also continue to run while not operating a safety lever. I definitely would not do this as the safety precautions are there to prevent potentially horrific accidents. One thing to bear in mind as well is the lawnmower won’t stop until it runs out of fuel!! I would never bypass a safety feature and neither should you. There is simply no need.

Lawnmower Has A Kill Switch And No Brake-Help

I have a Masport 470 series petrol lawnmower. I live in the UK and it was originally purchased in Australia. This lawnmower has a kill switch fitted but no brake. On a lawnmower such as this fitted with a Briggs And Stratton 450E or 500E engine, you will find the kill switch situated behind the petrol tank if the lawnmower has no brake system. If it has a safety brake it will be in the usual place at the back of the flywheel.

Lawnmower Kill Switch Common Mistakes.

The most common mistake people make is presuming the kill switch is faulty. I would strongly advise you check absolutely everything else mentioned in this article as in truth kill switches rarely if ever, break.

You can find lots more information and start repairing lawnmowers for profit by checking out my online training here

Happy Mowing


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