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sam the tech
sam the tech , Small Engine Technician
Category: Small Engine
Satisfied Customers: 142
Experience:  I have owned and operated a small engine shop for 10 years. Certified tech. for Briggs,Kohler,Honda,Kawasaki
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My John Deere 318 tractor has an electrical problem. The engine

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My John Deere 318 tractor has an electrical problem. The engine will run, but the PTO cannot be engaged without killing the engine. Also, when the travel lever is engaged, the engine is killed. The PTO light is illuminated without being engaged, when the key switch is on. This should not be either.
I have by-passed the seat safety switch. I have replaced the PTO switch, the key switch, the neutral safety switch, the module, and have visually inspected all the wiring and have done continuity tests on all except the lighting wires. I know that I must be missing something. Do you have any suggestions? Thanks in advance for your help.


There will also be a safety switch on the brake pedal. I think you are on the right track with the safety switches...your symptoms sound just like a faulty safety switch. You can test your saftey switched with a multimeter set to test for continuity. The two blades on your switch should show zero continuity, or Open Line (OL) until you push the plunger and you should have continuity. If you don't have continuity at those two blades with that plunger pushed in, then your switch is bad. Check that brake pedal switch and let me know what you find.



Customer: replied 6 years ago.
My JD 318 tractor has mechanical brakes that has no switch. When the brake is applied the travel control lever retracts to neutral.

Ok, take a look at this diagram. Ref # XXXXX in the diagram is identified as a brake switch and #54 is a brake switch connector. If you've bypassed both your seat switch and your neutral start switch(#33), then try testing for continuity, or bypassing the brake switch.


try that and let me know what you find.



Customer: replied 6 years ago.
I have the JD Technical Manual as well as the JD wiring schematic in front of me and neither one shows or mentions a brake switch. I see it on your drawing, however, but I need to know the colors of the wires that feed it so I can look for it on my tractor. Can you tell me the colors of the wires I should be looking for?

The diagram does not provide that information, and I doubt if bubba or jim bob at the local dealership here in my town could tell me either. Your brake pedal arm is physically pushing that plunger in to engage the switch. See if you can follow the brake pedal arm to find it. You'll want to avoid doing this if possible, but removing the mower deck(if applied) may make finding that switch a little easier. Also, jacking the front end up in the air will make it easier as well. I think if you did have a color coding to work with, you'd find once you get to a connector, the corresponding wire would change colors on you anyway...not always the case, but often find that they;ll change wire coating colors that meet at a connector. Follow that brake arm and you'll find that switch.


Customer: replied 6 years ago.
It's now midnight and about 0 deg. so I'll wait until morning to check out the brake switch that you identified. I hope you are right and that is the problem.
Just to be certain that we are on the same page, my tractor is the JD 18 horse onan, 3 series garden tractor with hydrostatic drive and power steering.

I looked up the JD model you provided. The diagram in question is for your model 318 JD. Let me know, thanks,


Customer: replied 6 years ago.
My tractor is apparently an older model (1984) and does not have a brake switch. I called the dealer where I bought it to verify it and he confirmed that there is no brake switch. The brakes are totally mechanical and when the brake pedal is depressed it simply moves the travel lever back to neutral.
Do you have any other ideas that I can try? Thanks much for your help.

My experience in the past with seat switches on JD mowers is that they are typically harder to bypass due to sometimes having more than two prongs and wires to deal with. You might try replacing that seat switch. Your problem is SO typical of a saftety switch that I am having a hard time thinking of anything else that would make it behave the way it is. Try a new seat switch, and if that doesn't work for you, let me know and I'll opt out of your question and open it up to other experts here on Justanswer that may be better educated on this than I. Let me know how it goes.


Customer: replied 6 years ago.
The seat switch has been by-passed by crossing the wires ahead of the switch. It is no longer an issue as there is no current going to it, as if it doesn't exist. That was the first thing I did to correct the problem, since it was the most likely and the easiest to do. And, the seat switch being bad would not make the PTO light stay illuminated whenever the ignition switch was turned on, and then cause the engine to quit when the PTO was engaged.
We are missing something somewhere...........

Ok, I follow you, but I am at a loss myself so I am going to opt out of your question and open it up for other experts to take a stab at...they will have access to all of the posts you and I have had up to now, so they'll be up to speed on what we've tried already. I'm sorry I couldn't help, and I hope one of the other experts here on Justanswer will be able to nail your issue down.


Reading through this thread, one thing bothered me -- your statement about bypassing the wires in front of the safety switch so there was no current flowing to it. Can you elaborate on this just a bit, please?

I am Still betting on a bad seat switch or a wire to the seat switch.


Humor me.. Test the seat switch with a meter. Is there current when the seat switch is pressed? IS there no current when the switch is not presses.


Correct me if I am wrong, but is the switch not supposed to be OPEN when pressed and shorted when the switch is not pressed. If this is the case, then shorting the wires to it would be mimicking having someone off the seat? Therefore making it not work?


I have not had much sleep, but could be backwards.



Customer: replied 6 years ago.
The switch is open with no one is on the seat. By splicing the two pink wires it therby closes the circuit all the time rendering the seat switch useless, which is what I have done. Consequently, the safety aspect of the seat switch is comprised. (usually not a smart thing to do but it eliminates one potential problem) In other words, splicing the wires mimickes having someone on the seat all the time.
The biggie in my mind is that the yellow dash light is on when the key switch is turned on without the pto switch being engaged. The only time the yellow light should come on is when the pto switch is engaged. THIS IS NOT RIGHT! When the pto is then engaged, the engine is killed.
Still stymied..........
Perhaps I'm wrong on your model, since I don't have a schematic, but every seat safety switch I am familiar with DOES NOT have current running through it. It functions only to ground the ignition module when the seat is not occupied (closed) and to break the path to ground (open) when it is. If your circuit functions that way (unless it is triggering a relay perhaps?), by bypassing the switch (rather than isolating the switch), you would cause the ignition to ground out whenever you engaged the PTO switch to complete the circuit.
Do you by any chance have a schematic you could post so we can verify this?
Customer: replied 6 years ago.
I have a schematic but I'm not sure how I can post it. I'll try and get it to you.
Customer: replied 6 years ago.
I am looking at the schematic now and it shows the switch as open, in agreement with your view. By closing it permanently via the by-pass I did, won't that eliminate it from being an issue in this problem?

Unless I am very mistaken about your circuit configuration, it would do just the opposite. Closing the switch would complete the potential path to ground, so it would be the equivalent of never being in the seat. Once the blades are engaged, the ignition coil would ground out and cause the engine to die, which is what I understand is happening. You want to "open" the seat switch rather than "close" it to test it. You want to prevent the circuit from reaching ground through that path.



Customer: replied 6 years ago.
In the past, when my tractor was "normal", whenever I wanted to watch the mower or snowblower operate without my being on the seat, I would jumper the
wires that go to the seat switch together, and start the engine and engage the PTO. The engine would then run, as well as the mower/blower without my being on the seat.
Isn't the jumper I used to perform said function the same as permanently jumpering the wires to the seat switch? Please convince me that my thinking is flawed and I will change whatever I need to solve this riddle. Thanks........

As I said, I may be wrong since I'm not a John Deere guy, and they're pretty protective about their info. The ones I'm familiar with use the seat switch to ground. Here's a schematic that will show what I'm talking about. Your's may be different. As I said, I'd sure like to see the schematic to know for sure.


You can see in this one that the seat switch normally is closed and provides a potential path to ground that is completed when the PTO is engaged (follow the path of the yellow wire from the armature). When the seat is occupied, the switch will open and break that path so the PTO can be engaged and the engine still run. Some wiring harnesses I've seen will be built with shorting clips that come together if the switch is removed to defeat the possibility of a user just pulling the switch out. If yours works like this you will need to open, not close it.






You are right the seat switch wires need to be wired together to bypass the switch. When did this problem start? With the tractor not running turn the key to the run position and engage the pto switch. Does the light go out? Can you hear the pto engage? What module did you replace (part number)? What is the serial number of the tractor and does it have single or dual pto.


Customer: replied 6 years ago.
This problem started 2 weeks ago while I was blowing snow. After about 1 hour it quit and would not start. The light does not go out when I engage the PTO, and I cannot hear the PTO engage. The module is the TIME DELAY CONTROL MODULE. The serial # XXXXX XXXXX and it has a single PTO.


Sorry i retired last night before you got back to me. The pto light being on and engine shutting off sound like to different problems. First lets try and fix the shutting off part. You should have to fuses one with pink wires and one with red wires. Check the one with red wires for bad fuse, melted holder, and corrosion. If that looks good turn the key to the on position and check these points for voltage with back wire of tester connected to a good ground. At key switch, red wire going to fuse. At module plug, prong with one red wire and one pink wire. Seat switch wires. At module plug, single pink wire. Let me know were you have voltage. And are all the connectors and plugs still original.


Customer: replied 6 years ago.
Hi Sam; The correct serial # XXXXX XXXXX; sorry about the mistake earlier. The fuses check out OK and are not corroded. The connections and plugs are original and have not been altered in any way.The engine will start and run perfectly.
I willget back to you with the test light answers as soon as I can get them. Thanks


I will wait till i you get back to me.


Customer: replied 6 years ago.
Hi Sam;
The fuses are OK.No corrosion or damage, orignal conditon. I checked the continuity using a probe light from a ground with the key swirch on, as you directed, and the results are as follows: Red wire from key switch to fuse has power. Module plug, red & pink wires, no power. Seat switch wire, no power. Module plug-single pink wire, has power. Please tell me what to do next. Thanks, Joe


Test results are a little odd since you have power at each end of the circuit but not in the middle. But maybe it can back feed through the module so unplug the module and redo tests. It looks like it might be a bad fuse box or the red wire that runs from the fuse box to the module plug (red and pink wire) is pinch off somewhere. If tests are the same except no power at pink wire take a safety pin or something and poke it through the wire about a inch or so back from the fuse box and check pin for power. Do it to both wires from fuse box if you do not have power on both wires the fuse box is bad. Let me know what you find.


sam the tech, Small Engine Technician
Category: Small Engine
Satisfied Customers: 142
Experience: I have owned and operated a small engine shop for 10 years. Certified tech. for Briggs,Kohler,Honda,Kawasaki
sam the tech and 3 other Small Engine Specialists are ready to help you
Customer: replied 6 years ago.
Hi Sam; With the module unplugged, I get exactly the sme results as before. What next? Joe
Customer: replied 6 years ago.


Hope everything works for you. Let me know.


P.S. If you are satisfied with my help please hit the accept button so i get paid for my time. Thanks

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