Mower Only Starts When I Jump Solenoid? (Why + What to Do)

There’s nothing more frustrating than having to switch your mower on, open the hood, and use a screwdriver to fire up the engine. And if anything, it’s a bit dangerous. If this is your current method, then you are jumping your solenoid. While this certainly works, it’s definitely not a convenient way of starting your lawn mower every time you want to use it. So, instead of putting up with this annoying process, let’s take a look at why your mower only starts when you jump the solenoid and see how to fix it.

Why Does My Mower Only Start If I Jump the Solenoid? (The Short Answer)

The starter solenoid is an electromagnet that is energized by a control cable connected to the ignition. The control cable circuit can become damaged and fail to give the solenoid the necessary power needed to activate and become energized. In addition, the internal components of the solenoid can wear down, resulting in a break in the starter electrical circuit. Jumping is a manual method to bypass the task of the solenoid.

Mower Not Starting Unless You Jump the Solenoid (4 Possible Reasons)

Within the starter circuit, there are several components that can stop your lawn mower from starting. So, let’s go over how you can diagnose which part is at fault.

Ignition

The ignition is responsible for providing the starter circuit with the temporary power needed to activate the starter solenoid. Therefore, if there is a fault with the ignition, the activating power will not reach the solenoid.

To test if the ignition is causing the problem, you need to test the output voltage of the ignition. So, take a multi-meter and connect the ground to either the lawn mower’s frame or to the battery’s negative side. Then, connect the positive side of the multi-meter to the starter terminal of the ignition switch.

Once you have everything connected, turn the key and test the voltage on the multimeter. If you’ve got a 12v mower, then you should see a 12v reading confirming the ignition is providing the required power. If the reading is under 12v, then you’ve found the root of the problem.

Control Cable

There is a control cable that connects the ignition to the solenoid. If this cable gets damaged, like there is a break, then it will lose continuity. If this happens, then power will not be able to reach the solenoid.

To check the cable, you can test the continuity or the voltage. Now, all multimeters have voltage testing, but not all of them can test continuity. Therefore, we’ll use voltage to check the control cable. To do this, connect the negative side of the multimeter to the negative battery terminal, then connect the positive side of the multimeter to the furthest cable end away from the ignition.

Now, turn the ignition to start and check the reading of the voltage. Again, you should see a reading of 12v for your 12v lawn mower.

Terminal

If you look at the terminals, you will see a number of connections on the various components of the starter circuit. If any of these are loose or corroded, then the electrical circuit will be broken.

To test the terminals of the starter circuit, you will need to use a multimeter. Connect the negative side of the multimeter to test the incoming power against the outgoing power. You should be getting the same voltage going out as the voltage that is coming in.

If you see that there is a drop of voltage or no voltage at any point, you will have diagnosed the potential cause of why the solenoid is not working.

Solenoid

Inside the solenoid is an electromagnet. When power is provided to the electromagnet, the plunger inside the solenoid moves and completes the circuit between the battery and the starter motor. Inevitably, these parts wear down over time and can no longer complete the circuit.

In addition, the mechanism of the plunger can wear down and jam up. This deterioration process can be slow, which is why you’ll find that the starter solenoids can sometimes work on and off.

So, if you have tested everything else in the starter circuit and the solenoid is receiving the power to energize, then you’ll know the solenoid is at fault.

How to Fix a Mower That Won’t Start Without You Jumping the Solenoid

If you find that you are not getting the reading you were expecting during your testing, then you’re one step closer to resolving your starter problem. So, here are my fixes to overcome your mower only starting when you jump the solenoid.

Replacing the Ignition

Modern riding mowers, like Craftsman, have quick disconnect ignitions that are common on many riding lawn mowers. It will take you no time at all to change these types of ignitions, and you won’t need any tools either.

So, start by removing the main battery fuse and then remove the ignition key. Next, lift up the lawn mower’s hood and find the ignition behind the mower’s dash. For the quick release, you will need to squeeze the tabs on the back of the ignition. It’s a bit fiddly, but if you squeeze the tabs and push the ignition, you should be able to push the ignition through the dash.

Once you have the ignition free of the dash, you’ll see that it is connected to the wiring loom with a large connector. So, pull off the connector and attach it to the new ignition switch. Next, press the new ignition through the dash so that it clips into place. Finally, close the hood and refit the fuse. This is all you need to do to replace the ignition.

Tools & Parts Required

• New Ignition

Replacing the Control Cable

To replace the faulty control cable, you have two options. You can either replace the individual cable or completely replace the ignition wiring harness. Now, as ignition harnesses are not all that expensive, I recommend you replace the whole thing. That is, unless you happen to enjoy electrical work.

So, to swap out an ignition harness, all you need to do is disconnect the individual connections and connect the new harness. I suggest that if this is the route you are going to take, then swap out one connection at a time. Doing it this way will prevent any confusion and wrong connections.

Tools & Parts Required

• Small Socket Wrench Set
• Pliers
• Screwdriver
• New Ignition Harness

Cleaning Up the Terminals

To clean corrosion on the terminals, you need to get hold of a small wire brush and some electrical contact cleaner. Start by disconnecting the battery, then grab the cleaner. Give the terminals and connections a good spray with cleaner and allow a few minutes for it to do its work.

Once the cleaner has soaked in, take the wire brush and brush off the affected areas. You will probably need to apply a few sprays of the cleaner for it to do a good job and remove all of the corrosion.

Once you have cleaned the terminal and connector, double-check how they fit. During your diagnosis, you may have found some loose connections. You might find that pinching the connector with a pair of pliers helps to get a tighter fit.

Also, for connections that require a nut and washer, check to see that the washer hasn’t totally flattened out. A lot of electrical connections on lawn mowers use tooth and split washers so that they stay in place with all the mower’s vibrations. So, if they don’t look any good, swap them out.

As a safety precaution, be aware that corrosion on batteries can burn your skin, so it would be a good idea to wear a pair of protective gloves.

Tools & Parts Required

• Electrical Contact Cleaner
• Small Wire Brush
• Pliers
• Replacement Washers
• Small Socket Wrench Set
• Screwdriver
• Protective Gloves

Replacing the Solenoid

Ride-on lawn mowers, such as Gravely and John Deere, use an inline starter solenoid that bolts to the frame of the mower. This is very common for ride-on, tractors, and zero-turn lawn mowers. So, if you have this type of starter solenoid, this is what you are going to have to do to swap it out.

First, disconnect the cables from the battery and tuck them out of the way. Then, take a socket wrench and remove the nuts holding the cables to the solenoid. Next, remove the mounting bolts that hold the solenoid to the frame of the lawn mower. Once these bolts have been removed, the old solenoid should come free from the mower.

Now, grab your new solenoid and bolt it to the mower using the same bolts that you previously removed. Then, attach the electrical cables to the solenoid and tighten the nuts using your socket wrench. Finally, reattach the battery cables and give the lawn mower a try.

Tools & Parts Required

• New Solenoid
• Socket Wrench

If you successfully diagnosed why your mower only starts when you jump the solenoid, these fixes should stop you from having to use a screwdriver instead of the ignition key.