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I recently inherited an STX 38 Yellow Deck Lawn Mower. The machine looks very clean. The engine is a 12.5hp Kohler. It's a 5-speed transmission. It runs great, except the electric PTO will not engage. Once I received the mower I drove it around the yard. Everything seemed fine until I switched on the electric PTO. It sounds like it wants to engage but it will not. The original PTO switch was severally corroded. I cleaned up all the wire ends and replaced the switch with a brand new one. It still will not engage. I got to looking today and found a wiring nightmare on the right side of the mower, near the large grounding plug, if you are sitting in the seat. There is a very heavy black cable attached to the frame in the same general vicinity. I'm sure that is the ground. I have a yellow wire with a small two male round prong clip. Then I have a small black wire coming from the large grounding point to a wire nut that has another black wire going back to the yellow wire with the small two prong plug. Then the third black wire tied with the other two then goes straight to an odd looking connector that has 1 spade going one way and the other spade going another. So one horizontal and one vertical. This connector end plugs directly into the female end that is attached to the electric PTO. I'm guessing this the area of concern but I am not 100% sure. The Tech Manual I have for the mower shows the Yellow Wire and the Purple Wire going to the electric PTO. I have a yellow wire but it has a small 2 round prong end on it with a black wire going into it. I'm not finding a purple wire in that area. But, I remember a purple wire on the new electric PTO switch. Everything else is top notch from what I can tell. New spindles on the deck. I installed a new deck belt yesterday. Yes, I hooked the PTO belt back up properly. Looking for suggestions, thoughts, advice, perspective or anything else anyone has to add. I sure appreciate it. Thanks in advance.

You need to give us more info before we can help you as wire colors mean very little on older units. We need to know: Make, more than yellow deck. Model and serial numbers, so we can see if there is a wiring diagram. Your electrical skills and understanding, so we know what terminology to use. Do you understand solenoid, NO safety switch, NC safety switch, relay, wiring diagram. Electrical troubleshooting can be a real pain, especially if you lack good electrical skills, so please help us help you by painting a picture of what you are looking at. Such as, if you have a diagram the red wire goes from the large terminal on the solenoid to the B terminal on the key switch. A diagram will tell you which component each wire should go to and if there are any junctions in between. Waiting to hear back.

If you have the JD technical manual for the STX then you can not do any better.
IT would appear that electricity is taught as badly in USA schools as it is down here thus it confuses 99% of the population.
This includes a lot of both professional & home mechanics who do all sorts of butchery to cars trucks motorcycles & lawn mowers.

The good thing is the JD manual shows you where to test a plug or switch as well as the colours of the wires that should have been there.

The PTO switch acts as a switchboard for most of the kill wire circuits, thus all of the black wires.
Check your wiring diagram and you should have a blue wire coming out of the PTO switch which should be the switches 12 V for the PTO,

Check the PTO clutch by jumping that wire to the battery +
If that does not work then jump the - wire as well.
If that does not work then your PTO clutch is faulty, out of adjustment or has broken wires.

Get back when you have done the testing.

I apologize for the lack of information. This was my first post on here. I am used to the Truck Forums where some information is just implied. This is a John Deere STX 38 with the Yellow Deck (the newer generation of this model had a black deck) headlight package was optional on this model and mine does NOT have headlights. Serial#(Product ID Number) MOOSTXB611787, it has a 38" deck. My level of understanding electric components and terminology would be above moderate/average but not expert. I understand wiring diagrams and use a Volt Meter on a daily basis. I finally had a chance to scan the Technical Manual to find the exact diagram I believe I need. It looks like someone has done less than a quality job on this "wiring" job. I checked my notes versus the Technical Manual I have the correct wires at the Ignition Switch and going to the PTO Switch. I need to open this back up to verify I have the correct wires leaving the corresponding switches. It is currently 10pm here in Ohio so I won't be able to do any Voltage checks/tests until tomorrow. I will let you guys know what I find out. Thanks for the information.

Well, I guess I should have stayed in bed today! In response to Rivets and bertsmobile1. Here comes the information.

I have already installed a new PTO Switch. (the original was corroded and not operational) Battery Terminals have been cleaned and I have a good solid connection.
I tested via the John Deere Technical Manual 4-56,4-57,4-58,4-59 (3/21/97)

1. Battery Voltage with Ignition Switch on and PTO Switch on - 11.77 Volts (in the manual normal operating range is 11.8-13.2 volts)
2. Key Switch terminal A on testing "400" Yellow Wire - 11.66 Volts
3. Key Switch terminal B on testing "200" Red Wire - 11.71 Volts
4. PTO Switch on testing "400" Yellow Wire - 11.57 Volts
5. PTO Switch on testing "750" Blue Wire - 11.52 Volts
6. At the PTO Clutch Connector with Ignition and PTO Switch on "750" Blue wire - 12.37 Volts
7. Across the terminals at the PTO Clutch Resistance measured 3.5 ohms (in the manual normal operating range is between 3-10 ohm)
8. PTO Clutch "125" Black wire resistance measured .0-.1 ohm (in the manual Maximum is .1 ohm) (in the manual it also states "If Not Normal" Check PTO clutch "125" black wire engine ground circuit, and battery negative cable ground connection) I did this and showed 0 ohms.
9. The fusible link is good I pulled the fuse. Now in the pictures, the fusible link is connected to a Purple Wire with Black Stripe. That is not on the PTO Circuit Diagnosis Section that I have.
10. There is a Purple wire that comes out of the PTO Switch.
11. I know this wire looks faded in the picture but the Purple Wire with Black Stripe goes to the Starter Solenoid. Along with the Red Wire.
12. I took a picture of the PTO Clutch Connector. Several different looks. Is that the correct connector?

Now with it whisper quiet in my backyard this afternoon, when I switched the Ignition Switch on and then the PTO Switched to on I heard the "PTO Clutch Noise" or clap, whatever we all can agree on. Still scratching my head, I started the tractor it was running fine. I switched the PTO Switch On and once again it acted like it wanted to but nothing happened. So, I shut it down and came in here to post all the info I had. I have the complete manual so I can look at other diagrams. It's about 360 Pages so I would need a starting point. Thanks in advance for any and all assistance. bertsmobile 1 you are correct, they "teach" "us" just how to get it going method here in the United States. Then guys like us are left to "Fix it Right"! On a side note, I would love to visit Australia someday! It's on the bucket list, but that 17-hour flight might be a deal breaker.

By the time I had done all that you have I would taken off the clutch and tested it first, that way you would know that the clutch is working or not, before going into wiring and switchers.

EngineMan - Thank you. Fortunately or unfortunately depending on your perspective, I have nothing but time!

Possible the air gap on the clutch. Have you checked to see if the spindles turn free when belt is off.

Luffydog I can't say I even thought of that. Thank you! I will check it out tomorrow sometime.

i agree with engineman i think you should take the clutch off check air gap apply voltage and also check bearings

OK folks why not run around and check the left rear tyre then the steering bearings follower by the brake pads.

The man has the JD technical manual and is working through it in a methodical mannar, why not let him do it rather than running him from pillar to post in a random fashion ?

Don't guess u have an attitude problem or anger management issues with others trying to help. Sometimes the manual don't always help out for the issues at hand so running post to pillar might not be a bad idea at times never hurts to have a backup plan other than the manual.

No I don't and I don't have an ego problem either.
Having taught ( nothing to do with mowers ) for several years I came to understand just how confusing simple things can be to those with little to no understanding of them.
All of us have a method to solving any particular problem and all of them work or we would still have the problem.
Having a dozen people all chiming in with their our variations on the same theme 1/2 way through a systematic diagnosis does little other than to confuse.
If some one has gone to the extent of obtaining a manual then it is best to let them work through it and limit oneself to explanations of what the poster does not understand.
Or point them to the relevant section of the manual.
There is no better manual than those published by JD as they both teach the why ( theory of operation ) and the how, thus the poster will know all when finished.

We all have different ways of approaching the same problem, I see none of them to be any more correct than others, they are just a different sequence usually because we are not trying to understand what is happening, just to get the mower out of the shop asap and back to the customer.

Thus when some one has taken up a persons problem I pass over it without comment ( usually ), avoiding the "too may chiefs" problem or if I do I try to carry on the line that the original helper has started on.

I have a copy of the same manual he is using and can see where it will lead.
He will get there in time and will have covered all bases. If you go back to the beginning of the thread you will see that BashRipRock has a dubious rats nest of bodged & confusing wiring which at some time he will need to come to grips with, thus we have started by confirming the wiring.

I apologize for my misbehavior and not being professional about it. Yes I did read that but when he said he got the clutch to work and could hear it click and it turns on I figured he had the wiring problem worked and I thought he might have had other issues other than power. Again I apologize for not being professional and taking things wrong way.

Folks: I in no way wanted my post to turn into some issue debated around the WORLD. I appreciate all suggestions and will not pass judgment on anyone. I also appreciate the support while I work on this matter. If I lived in a perfect world I would own a Brand New John Deere. My current situation does not lend me to do that. I was given this mower at No Charge. I am currently out the cost of an Air Filter Element and a New PTO Switch and maybe a gallon of fresh gas. I have spent some time just cleaning up the mower itself. I do not need this mower to mow my yard or operate my business. I was more interested in using the tractor to pull my lawn cart to pick up limbs, leaves, etc.
Let me explain my background. I am a 42-year-old father of a 3.5-year-old son and happily married. I have a 4 year Degree and some Post Graduate work. I worked in the Agricultural Science Field for about 15 years. I grew up on a working farm so we learned to fix "everything" around. From there, I took the position as Technical Service Manager for a large medical device company. After 7 years of that I decided to work for myself. I am very Tech savvy, have an average or above average understanding of electronics and how to test them. I am very methodical in my method. Like I mentioned in a previous post, "I have the time." I was just reaching out to this forum for assistance with my situation. I do have the Tech Manual from John Deere. It is, and has been very helpful and insightful. The Theory of Operation is a real nice addition. I want and like to learn as I am doing. I did not have time today to get anything checked out on the mower. I am hoping to get time tomorrow. Because, I would like to get it figured out and move on to another project.
I will continue to post updates and I welcome all comments, thoughts, or suggestions. But with all due respect may I suggest to everyone that they please read all the posts and follow-ups to provide accurate and current situational information.
I know I sound like a broken record. I do not or did not want to offend anyone by joining this forum. Luckily I have the ability to take it all with a grain of salt. I do want to say to bertsmobile1 Thanks for having my back. You said it perfectly. I am not picking favorites or anything like that. I sure hope as adults we can have a casual cordial discussion on assisting people with their questions concerning John Deere Lawn Mowers. I will try to post an update on the mower tomorrow instead of a personal response to the forum. Thank you all for listening and the support.

Don't fret any.
There are very few responders here with glass jaws.
If they had one it would have been chards on the floor a long time ago.
Luffy is a bit new but he will settle down in due course.
It is frustrating if you believe you know what the problem is and you are being ignored.

Carry on carrying on.
JD had this thing about fitting fuseable links rather than a std blade fuse.
In time they all fail and some of the jobs of fitting a fuse are neater than others.
I for one always fuse both the battery and the alternator on separate fuses.
Then on some models they short the alternator to ground so it acts as a brake when turned off.

The wiring is actually quite simple it is just all of the things done to cut costs that make it confusing.
Then JD add to that by throwing in some relays just for the fun of it.

Thanks for the heads up about your background.
It makes it a lot easier if you know what level to pitch a reply to.

We have a mowing machine now! It needs some fine-tuning, some additional minor repairs, and parts replacement and she should be good to go. I have looked at the schematic till I was cross-eyed. Then by chance I was able to get in contact with the person I got the mower from. Well the long and the short of it is this. He was given the mower by someone to work on and he never got around to repairing it. He said that it cut the grass fine when he got it and never had a chance to move any further with it. So I am at least the 3rd owner. The person I got it from did not do the botched wire job. See the first photos if you so choose.

I took this new information, that it did cut grass, and ran with it. I checked the air gap on the PTO Clutch and it was spot on. I knew the electrical system was good from all the testing, so what was I missing? I had never been able to actually see the PTO Clutch turn. So with the help of my 3.5 year old son sitting on the seat, "yes he was safe for all those that may be concerned" I had the tractor running and flipped the PTO Switch on, looked down and the PTO Clutch was turning but the belt was not. Upon further inspection the belt was not on the back top pulley of the deck. Hence no blades spinning. I pulled the deck out to see what was going on. I found that the 3/8" Nut was missing from the long bolt through the bracket that applies automatic tension to the belts. It was extremely sloppy. I'm not sure how it never came apart? I got out my Tech Manual and also on JD.com and brought up the parts diagram and sure enough, there is to be a nut on that bolt. I didn't have the appropriate lock nut but I put on a nut that I had to see if this would help my situation. Got everything back together. Cleaning as I go. Now the moment of truth. Tractor started, I engaged the PTO Clutch and voila! I had grass blowing out the discharge chute. I took it for a little stroll around the property. It operated the way it was supposed to. Like I said it needs leveling, 2 new blades, a muffler "I found a hole it while climbing around, plus the smoke while I was mowing" and a few new pins, etc to tighten the overall machine up. I am still confused on the PTO Clutch wiring? When I get the time I will rework the wiring and solder new ends on so it looks more up to my standards. I can't say that it will run for hours on end but it ran good for 15 minutes. I am happy with that. I'm going to mow the rest of the yard tonight so if something happens or the wheels fall off I will let everyone know. This is not my best writing I'm in a bit of a hurry.
Thank you for all the information, help and insight. It is greatly appreciated. bertsmobile1 I would like to stay in contact. I'm not sure how you send private messages or what but if you know how and can I would greatly appreciate it. Talk to everyone later!

had that same problem with my 111 found out the spacer between the clutch and the engine was missing and it was shorting out the wires i made a spacer out of washers and fixed the problem.works beautiful now.

Green Dream, thanks for the input. I’m on my phone so I’m having difficulty doing this. Ironically my father bought a lot of tractors at auction around early summer if 2018. In there was a twin cylinder 116 I believe. Along with some other junk! The PTO on that unit was acting real funny. Switching on and off, etc. Talked to an ole timer around here and he said that the 100 series had this same issue you were describing. So, we machined a spacer to put in there. Now works perfectly. I appreciate you sharing your experience. I have received a lot of help on this mower forum and also on a snowblower forum. It’s nice we can kind of just help everyone out and try to keep the costs down on repairs! Have a good day! Thanks again!