Dear Ole Mechanic;Riding Lawn Mower

I know it is early, but during the last nice weekend I dug out the riding mower (in hopes that we might get some rain) and tried firing it up to pull the manure cart around.  I charged the battery and put in fresh gas, as I had drained the old gas out last fall--just like you suggested in your storage tips column.  I hopped on the mower, stepped on the brake/clutch, turned the key and--nothing.  No click, no crank, no chatter--nothing.  I checked the battery cable connections, but they were clean and tight.  I was standing there staring at the tractor when my wife came by and ask what was wrong.  I told her it wouldn’t start.  She hopped on the mower, turned the key on, turned on the lights, and then asked me if they had come on.  I said yes,--that they were on.  She turned the key to START and the engine fired right up!  To make a long story short, I hauled and spread the manure and then started trying some things.  Without turning on the lights, the mower wouldn't start three out of five tries.  If I tried the lights and they came on, the mower started four times in five tries.  The one time that the mower didn’t start, the lights went out and didn’t come back on until I turned the key on and off a couple of times.  There were three or four times that with the key on, the lights didn’t come on.  When that happened, the mower wouldn’t crank or start.  I thought about the battery, but if that was the problem, then it wouldn't ever crank and start.

How could turning the lights on have any thing to do the starting?  What is going on? 

Oh, the battery is only a year old and the mower is seven or eight years old.

Running with the Lights On


Dear Lights On;

Fortunately for you, I have seen this problem before--several times.  You have a contact problem either with the wiring connector on the back of the ignition key switch or inside the switch itself. 

OK, how does turning on the lights help start the mower?  There is a simple electrical explanation.  The starter solenoid uses a lot more electricity than the lights.  The sudden load of the starter solenoid causes the bad connection to break down and not let any electricity flow.  The lighter load of the lights helps establish a small connection that will allow a larger load to pass through, as the connection has already been established.

If the problem is in the wiring harness connector, sometimes just removing and replacing the connector will clean the connection, and it will work as it should.  The usual problem is not removing and reinstalling the connector, but getting access to the back of the switch where the connector is located.  Getting to the back of the switch on some mowers is not too bad, but others require a major disassembly of the mower.  If the switch part of the connector or the internal contacts is the part that has suffered the worst corrosion, it can be replaced.  It is not exactly a cheap repai,r but after you get to it, it is not a hard replacement.  If, however, the wiring connector is badly corroded, then you have a bigger problem.  The connector only comes as part of the complete wiring harness.  The harness is a big OUCH in the $ department--IF you can get one.  Depending on the make of your mower, it might be available, or it may have been discontinued and no longer be available.  If it is available, then replacing the harness can be a real headache, as the mower may require a major disassembly that includes removing the engine.  There are a couple of wiring repairs that be done instead of the disassembly.  One would be to get the new harness, cut the connector and enough wire on the harness to splice into the harness of the mower after the defective one is cut off.  Of course, that produces another place for corrosion in the future.  A cheaper repair would be to cut off the old connector close to the connector.  Cut one at a time and then put individual connectors on each wire and push each connector onto the switch separately.  The only problem with this repair is making sure the right wire goes on the correct terminal on the switch.

There is one other option, and that would be to replace the mower with a new one.  This option may be the most viable if your present mower was an "El-Cheap-O."  If, on the other hand, you have one of the expensive lawn tractors that has a mower attachment, a tiller attachment, a front or rear blade attachment, and so on, then a repair would be in order.  Also, lawn tractors usually have a better availability of parts and are more likely to have a local dealer or service facility that can repair your mower. 

For now, just clean the connection, keep hauling that manure and hope for rain. Either that or follow the advice of a friend of mine, “Why would anyone want to repair a perfectly broke lawn mower?  That means ya got to use it.”

Herr Professor Nuzanbolts