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Strange situation today. Wife could not get the mower to turn over even though battery read 12.47 volts. She suggested we try to jump start anyway? When we connected the jumper cables to a spare car battery the mower immediately started turning over even with they key in the off position and when removed? Engine was flooded so it wouldn't start but would the starter have even disengaged had it started, my guess not. We replaced the solenoid about 3 years ago. Any ideas on where to start troubleshooting? Key switch, solenoid again, other? Having a hard time finding search results on Google or Youtube when describing the situation. Help would be appreciated.

Where did you connect the jumper leads to ?

Ran jumper cables from the spare battery to the battery still connected within the mower like I've done a dozen times before. Positive to positive, negative to negative. As soon as I touch the positive post on the external battery it tries to start. Key in the off position.

Pull the control wire (s) off the solenoid and see if they are live when you connect the jumper.
IF the engine cranks with the control wires removed then the solenoid is jambed on ( never seen this happen before )
If the engine does not crank with the wires off then your key switch is bad or there is a short some where energising the solenoid, also rare.
IT would be really helpful if we know which engine is in your mower

Engine is a Kohler Command 16. Just changed the oil in it but don't see that would have anything to do with it. Drove fine from the garage to it's storage location under the house after that.

Remote starter solenoids can and do jammed in the on position. Especially when overheated from long starting periods.

This just gets stranger the more I screw with it. Clamped onto the loose battery cables (not connected to original battery) with jumper cables yesterday morning and it cranked with the key just like normal! Hooked the original battery back up and nothing happened. Seems that sometime overnight it had drained down to less than 6 volts from being hooked up so took it out and put it on the charger. Tried to replace the solenoid but they mounted it in such an usual way I couldn't get to the torx screws to remove it. No good Google/Youtube suggestions on how to remove it. Guess I will have to rip it out and find a more serviceable way to remount it? Took connections off old solenoid and hooked it up to new solenoid (which I just set in there in contact with bare metal) and tried jumping it again, nothing, maybe a grounding issue.. Hooked wires back up to old solenoid and hooked the jumper cables onto the loose battery cables and it again started right up. Put the original battery back in after charging and again it started right up as if nothing was wrong. Wife came how and mowed, starting and stopping it several times without any problem. Looks like it might have corrected itself but this morning will tell more when I go down to see if it will start after setting overnight. Guess my wife is going to have to wait awhile for a zero turn mower replacement, this Scotts is 20 years old now. Called several John Deere dealers about the problem to see if they had a definite idea on a part replacement. Their only suggestions were that it might be the solenoid or starter switch? It was like they had never heard of a mower cranking without the key in the proper position. Surely I'm not the first person to have had that happen?

Try wiggling the key in/out, up/down, and side to side while it’s in the ignition switch but in the off or run position (engine off). Could be an intermittent connection/short in the switch.

Ran down to check out the mower this evening and it started up without any hesitation? Does it again I'm just going to rip out the solenoid and find a better more serviceable way to attach the new one. $14 isn't much a repair cost if that was, or becomes the problem again. Would still feel better if someone could say definitely what caused it to act the way it did. Happy mowing, the grass if growing! Actually it's the weeds on my acre of ground, but at least most of them are green.

As others have pointed out, the solenoid must be receiving power with the key off to be engaging the starter - known as a short to voltage. If you understand how a basic relay works, the solenoid functions in the same way, so it must be getting power from somewhere in order to close the contacts.

Given the intermittent/odd conditions you’re seeing, I’m leaning towards the key switch or the wiring harness being damaged. You can use a test light in place of the solenoid to troubleshoot the key switch and harness.

I get your frustration with the solenoid location - I had a 1642 for several years and I didn’t like it either. I only replaced mind once, but when I did, I cut notches out of the bracket so that the screws only had to be a little loose and the solenoid could be slid underneath the heads. Then the screws only had to be tightened down a few turns - made installation much easier.

Still working fine as of today. Holding onto the solenoid I got from HD for a couple weeks just in case. Can you point me towards the procedure of testing the solenoid to see if the key switch is the problem? I'm assuming I'll have to wait till it starts malfunctioning again? Since the frame hole is threaded I'm going to resort to bolting the solenoid down from the top side when I do have to replace it. For a 20 year old mower it's been impressive. About the most I've had to do to it other than change the oil/filter is drop the transmission and replace a piece on it and replace one of the bar attachments on one of the front wheels. Just wish there was some way to put a wider mowing deck on it but JDeere said no way!

You don’t necessarily have to wait until it acts up again - it depends on what’s actually going on. But testing for a short should only take a few minutes.

Note: I say test light, but this will also work with a meter - just watch for battery voltage instead of the light turning on.

1) Disconnect the control wires for the solenoid.

2) Verify your test light is functional by checking it on the battery.

3) Connect test light between the control wires for the solenoid.

4) Key off, test for a short in the wiring by wiggling the harness, starting at the key switch and working towards the solenoid. While doing so, watch the test light to see if it flickers on and off - even a quick flash of light indicates a short. If the light turns on at any point, closely inspect that area of the harness for bare wires making contact. Clues of the problem are often marked by melted insulation. Repair as necessary.

5) If no problems are found, perform the same type of testing with the key in the switch. In the off position, move it back and forth and side to side to check for contact problems. What you’re trying to do is move the switch without actually rotating the key to on or start.

6) If still no problems are found, consider it fixed.

Wife went to start the mower this morning. She said that it cranked on the first try but did not start. On the second try, it started but she could still hear the whining noise (starter?). She turned the mower off and even pulled the key out but the whining continued. She grabbed a 10mm wrench and unhooked the negative from the battery to finally get it to stop. The negative cable was very hot, I guess from all the starter antics? Decided the next step would be to replace the solenoid (joy!) Spent about 3 hours trying to get it off but think I finally came up with the battle plan for removing it properly which is... Remove the right rear wheel. Use a blow dryer on the gray plastic cap to get it to come off with ripping. Once the wheel is off, remove the metal plate that the reverse sensor is mounted on. It's held in place with just one fat bolt. After that, playing with the deck height settings and the forward/reverse lever should open up enough space to go after the upside down screws that hold the solenoid in place. I used a 4mm hex bit and some extension rods and was able to get to both of them pretty easily after that. For the new solenoid install I shortened the 2 mounting bolts (had already screwed a bunch of the end threads from previous attempts at removal), set the solenoid on top of the frame and screwed it down from the top. That will keep me from having to take the wheel and switch off in the future. Anyway, it seems to be working like it should again so I'll keep my fingers crossed until the next mowing.

The usual method is to remove the battery then the battery carrier .
Still not exactly easy but a lot less work that you are doing .

Tried that first. Nothing to try and grab hold of except the screw threads. Finally succeeded in breaking the solenoid off by prying it back and forth. That took forever but it did give me better access to the threaded part of the screws. Tried cutting slots in the ends to use a screwdriver but that just broke one side of the screw off. Tried pliers and vise grips without success. They were on there really tight.

A litle grease on the threads of the new bolts is called for + a dedicated ground wire .

I’d recommend replacing the cables for the battery and starter. If they’re original and they’ve gotten hot, their ability to conduct current has certainly been reduced.