Electro-magnet On PTO Lever Issue

wirlybird · Jan 5, 2021

HI all,
This is on my 756 and I know wrong group but I think this could be a more generic question and apply to other Deere's so I am asking here.
With the tractor on/running the electro-magnet (yellow arrow) is supposed to be active so the PTO lever (blue arrow) can engage the PTO.
The part at the blue arrow is the PTO lever on the dash. The part at the yellow arrow is the magnet and the actual PTO linkage.
So, move the lever on the dash toward the front of the tractor and the part at blue arrow pulls the part at yellow arrow engaging the PTO. If a safety switch is activated then the magnet goes dead and the part at yellow arrow is released returning to the rear position shutting off the PTO.

Here is the issue!
The magnet isn't working when plugged into the wiring harness.
Test the plug on the wiring harness with magnet unplugged and key on and there is 12 volts.
Apply 12 volts to the lead from the magnet and it energizes and works correctly.
Plug the magnet lead into the wiring harness and with the key on you get NO voltage.

So, the magnet works with 12 volts applied via jumper wires but not when plugged to the wiring harness. It seems to kill the voltage at the harness.
Magnet show about 41 ohm resistance.

I tried messing with the seat switch and I can hear a relay like click when I push the switch so it seems to be working.
Any ideas?
I am thinking to just add a toggle switch and jumper to the magnet to energize it so it will work but really would like to understand what is going on and why the magnet kills the voltage at the harness.

CantKeepUp · Jan 5, 2021

With the wire connector not plugged in, there is no load and you read 12V. I assume that once you attached the magnet (load the 12V), the 12v plunges down to a lesser value. I would suspect that if you could read the voltage while connected, you would see that.

I'd guess that you have a bad contact or a bad ground.
I'm guessing the possible culprits are:
Seat Switch Contact
PTO switch Contact
PTO Control Module contact
Bad ground (you probably have a black(a random guess) wire going to the PTO magnet that gets grounded somewhere.)

Before you do anything else, you may want to pull the battery terminals and give them a good cleaning. I doubt that's your issue, but it would be a wise, easy, and free first step.

I don't know what a 756 is, thus the "guesses"

wirlybird · Jan 5, 2021

CantKeepUp said:
With the wire connector not plugged in, there is no load and you read 12V. I assume that once you attached the magnet (load the 12V), the 12v plunges down to a lesser value. I would suspect that if you could read the voltage while connected, you would see that.

I'd guess that you have a bad contact or a bad ground.
I'm guessing the possible culprits are:
Seat Switch Contact
PTO switch Contact
PTO Control Module contact
Bad ground (you probably have a black(a random guess) wire going to the PTO magnet that gets grounded somewhere.)

Before you do anything else, you may want to pull the battery terminals and give them a good cleaning. I doubt that's your issue, but it would be a wise, easy, and free first step.

I don't know what a 756 is, thus the "guesses"

756=755

Battery is good and clean.
Magnet has 2 wires that go to the connector (male) and both look ok. Since it is an electro-magnet there is no "ground". The orientation of + & - leads just determine polarity of the magnet.
Connector on the wire harness (female) has 4 wires into two connections, two Pos and two Neg and read 12V with key on.
12V from battery powers magnet ok.
I will put my meter in line and see if I can see the voltage drop.

Nouveau Redneck · Jan 5, 2021

So you are saying that the two connectors in the plug can reverse voltage to reverse the polatrity of the magnet, correct? That implies that the coil in the electromagnet is supposed to be totally isolated from ground so that the polarity reversing works. But you said that if you connect a single 12 volt wire to one of the connectors on the electromagnet that it energizes. That implies that there is some path to ground that it is finding. This is just a semi-educated guess, but it sounds like maybe the insulation on the coils in the electromagnet have degraded and that is causing a short to ground. Does the electromagnet energize no matter which connector you connect the 12 volts to?

wirlybird · Jan 5, 2021

Nouveau Redneck said:
So you are saying that the two connectors in the plug can reverse voltage to reverse the polatrity of the magnet, correct? That implies that the coil in the electromagnet is supposed to be totally isolated from ground so that the polarity reversing works. But you said that if you connect a single 12 volt wire to one of the connectors on the electromagnet that it energizes. That implies that there is some path to ground that it is finding. This is just a semi-educated guess, but it sounds like maybe the insulation on the coils in the electromagnet have degraded and that is causing a short to ground. Does the electromagnet energize no matter which connector you connect the 12 volts to?

No, not exactly. The factory connector only goes together one way and has a positive and a negative leads/terminals. So the female terminal/connector coming from the wiring harness has a positive and a negative connection. The connector coming from the magnet has two terminals in it and they are arranged so one plugs into the positive and one to the negative on the wiring harness connector. This creates the polarity of the magnet. If the two wires from the magnet were reversed when plugged into the connection from the wiring harness the polarity would reverse.
The polarity of the electromagnet is determined by the direction of the current.

So when I energized the magnet myself, to test if it even worked, I used a positive and a negative jumper from the tractor battery.

Make sense?!

wirlybird · Jan 5, 2021

So here is my solution for the time being to get the PTO working.
A fused lead from the positive battery cable, it had a spare lead, to my switch.
Negative from the battery and positive from the switch to the terminals from the PTO magnet.
Flip the switch, magnet energizes and then the PTO will engage. Flip the switch off and the magnet will release.
I may try to find another switch that fits better but for now it works.
Would still like to know what is causing the factory setup not to work.

Dave55 · Jan 5, 2021

I know nothing about your tractor, but I think I see an indicator light for PTO engaged on the dash.
Does that light come on with your installed switch?
Did it come on when it was hooked up the factory way when you moved the lever to PTO engage?
I really can not see power going to that magnet and the PTO indicator on the dash lighting as soon as the key is turned on, so there is probably a switch somewhere on the PTO linkage that activates the light and magnet when you engage the PTO lever.
Most mowers will not engage PTO unless someone is in the seat, another switch that can fail, and that safety switch most likely kills power to the magnet.

I know many mowers will not mow in reverse from the factory, so there would have to be a switch on the transmission selector to kill PTO power when in reverse, another possible failure point.
I have seen these wired to kill the motor if the PTO is engaged when you put it in reverse, I have seen it kill the PTO when reverse is selected, I have seen override switches that must be operated every time you select reverse to keep the PTO engaged. How John Deere did it I have no idea.

Good Luck

wirlybird · Jan 6, 2021

Dave55 said:
I know nothing about your tractor, but I think I see an indicator light for PTO engaged on the dash.
Does that light come on with your installed switch?
Did it come on when it was hooked up the factory way when you moved the lever to PTO engage?
I really can not see power going to that magnet and the PTO indicator on the dash lighting as soon as the key is turned on, so there is probably a switch somewhere on the PTO linkage that activates the light and magnet when you engage the PTO lever.
Most mowers will not engage PTO unless someone is in the seat, another switch that can fail, and that safety switch most likely kills power to the magnet.

I know many mowers will not mow in reverse from the factory, so there would have to be a switch on the transmission selector to kill PTO power when in reverse, another possible failure point.
I have seen these wired to kill the motor if the PTO is engaged when you put it in reverse, I have seen it kill the PTO when reverse is selected, I have seen override switches that must be operated every time you select reverse to keep the PTO engaged. How John Deere did it I have no idea.

Good Luck

Yes, there is a light for the PTO to indicate it is engaged.
This is a bit confusing so I'll try to explain.
There is a lever that comes up through the dash similar to the throttle lever. This lever simply moves forward and back. Forward being PTO engaged position.
This lever has that kind of disk or metal part shown by the blue arrow in the original picture.
There is a second "lever" or arm that has the magnet, shown by the yellow arrow. This is the actual mechanical mechanism that engages the PTO.
When the magnet is active the disk is attracted to the magnet which essentially connects the PTO lever to the PTO linkage and when you move the PTO lever forward it in turn moves the PTO linkage.
The PTO linkage arm is spring loaded so while the PTO is engaged if the magnets power is cut it disengages and the PTO linkage will release and return rearward to the disengaged position.

In normal operation once you are in the seat and turn the key on, or start, the magnet is energized so the PTO can be engaged normally.
Yes, I also believe there is a switch somewhere to make the PTO light come on when the lever is engaged. It works when you move the lever.
The issue is that the wires at the connector on the harness that is for the Magnet has 12v when the key is on as they should. However when you plug the magnet connector into the harness connector it kills the voltage and my test reads 0 volts and the magnet does not energize.
If I supply 12 volts, from the battery, to the wires that go to the magnet it works fine.
So for some reason, which I have not found, plugging the magnet into the harness as it should be kills the voltage that should be supplied to it.

So, all of that to say that when I got this tractor someone had zip tied the two levers together in the location of the magnet so that when you move the PTO lever it would move the arm. Basically a mechanical link to bypass the magnet. Zip ties don't do well in cold weather and broke!

Hope it makes a little sense.

Nouveau Redneck · Jan 6, 2021

So when I energized the magnet myself, to test if it even worked, I used a positive and a negative jumper from the tractor battery.

Make sense?!

Thanks for the clarification. Sorry I misunderstood originally.

Could there be some other safety mechanisms in the circuit that you don't know about like a seat switch or brake pedal switch? Seat switch would only allow the PTO to run when it sensed weight in the seat and brake switch would only allow it to run when it sensed that the brake pedal wasn't engaged. If either switch exists and is faulty that could be the problem.

Dave55 · Jan 6, 2021

A digital volt meter will display voltage at a level so small that it is not useful. Example, Yes you have 12 volts, but there is only .0001 amps there. In this example 12*.0001= .0012 watts. a 194 Side marker light bulb is rated at 14 volts .27 amps and 3.78 watts. .0012 watts would not even start to make that light filament start to turn red. So even the smallest light bulb would not light with that amount of current.
In this instance a test light may be better than a volt meter to detect current.
I have some friends that are mechanics full time. They made a test light to diagnose problems like this using a 3156 tail light bulb and socket with some long wires connected to the leads. A 3156 bulb will take 2.1 amps to light and that might be enough power to make the magnet work.

A. If you have a test light, is there enough power at that connector to light a test light going from the positive to negative terminal of the connector?
B. Will a test light light between the positive connector terminal and battery ground?
C. Will a test light light between the ground connector terminal and battery positive?

1. So right now when you flip your added switch to ON, does the dash PTO light come on when you engage the lever?
2. If you plug the stock wiring back in, when you move the lever to engage does the PTO light come on if you hold it to engage position?
3. Somewhere on the linkage you are moving with your hand, there has to be a switch that turns the dash light on and engages the magnet.

My guess is that switch is the problem, or the wires going to that switch is the problem.

Hopefully A, B, C tests will show you have enough power to light a light bulb at the connector.
Electrical problems are never fun, but you have to start somewhere. I also will guess that at least one test of A B C will result in a no.

You are a little to far from me for me to stop by.

I am a little confused about the zip ties.
Did you have to hold your hand on the lever for the PTO to stay engaged?
Or did the PTO engage as soon as the engine started?

wirlybird · Jan 6, 2021

Nouveau Redneck said:
Thanks for the clarification. Sorry I misunderstood originally.

Could there be some other safety mechanisms in the circuit that you don't know about like a seat switch or brake pedal switch? Seat switch would only allow the PTO to run when it sensed weight in the seat and brake switch would only allow it to run when it sensed that the brake pedal wasn't engaged. If either switch exists and is faulty that could be the problem.

I am wondering about that. So far have not found anything.

Dave55 · Jan 6, 2021

Found a wiring diagram.
Everything is in the lower center to left corner.
Looks like there are two 10 amp fuses, top and second fuse that get power from the ignition switch.
Top fuse goes to ignition position on switch.
Power out of fuse goes to PTO indicator light on dash, then goes to PTO Lamp switch and then to hex 1 to complete circuit.
Wish I had a little more detail on the drawing, symbol hex 1, hex 2, hex 3.
I see seven hex 1 symbols, one of which is also labeled engine ground and the one by the ignition switch which appears to be hooked to the ignition switch ground.
I see two hex 2 symbols, with no other marking by any of them.
I see one hex 3 symbol that also has a normal ground symbol by it.
Second fuse is powered from ACC position on key switch.
Power out of that fuse goes to the Operator Seat Switch, if closed then it goes on to PTO selector switch.
From what the drawing is showing if you have the rear PTO only selected, the seat switch and PTO selector switch are the only switches involved to energize the magnet.
If you have mid and rear PTO selected the control module, operator seat switch and the PTO selector switch are all involved.

On a side note, in your first picture in the top left of the picture is that the connector for the magnet?

If so is the right side terminal the positive terminal?

bogieboy · Jan 6, 2021

on that drawing, the hexes are ground point. 1 is the engine ground point, if you notice by the battery, 3 is your chassis ground, number 2may be specific to your pto circuit, i dont see a call out for 2..

wirlybird · Jan 6, 2021

Dave55 said:
A digital volt meter will display voltage at a level so small that it is not useful. Example, Yes you have 12 volts, but there is only .0001 amps there. In this example 12*.0001= .0012 watts. a 194 Side marker light bulb is rated at 14 volts .27 amps and 3.78 watts. .0012 watts would not even start to make that light filament start to turn red. So even the smallest light bulb would not light with that amount of current.
In this instance a test light may be better than a volt meter to detect current.
I have some friends that are mechanics full time. They made a test light to diagnose problems like this using a 3156 tail light bulb and socket with some long wires connected to the leads. A 3156 bulb will take 2.1 amps to light and that might be enough power to make the magnet work.

A. If you have a test light, is there enough power at that connector to light a test light going from the positive to negative terminal of the connector?
B. Will a test light light between the positive connector terminal and battery ground?
C. Will a test light light between the ground connector terminal and battery positive?

1. So right now when you flip your added switch to ON, does the dash PTO light come on when you engage the lever?
2. If you plug the stock wiring back in, when you move the lever to engage does the PTO light come on if you hold it to engage position?
3. Somewhere on the linkage you are moving with your hand, there has to be a switch that turns the dash light on and engages the magnet.

My guess is that switch is the problem, or the wires going to that switch is the problem.

Hopefully A, B, C tests will show you have enough power to light a light bulb at the connector.
Electrical problems are never fun, but you have to start somewhere. I also will guess that at least one test of A B C will result in a no.

You are a little to far from me for me to stop by.

I am a little confused about the zip ties.
Did you have to hold your hand on the lever for the PTO to stay engaged?
Or did the PTO engage as soon as the engine started?

Great suggestions and I'll try to address your ideas point by point.

Here are a couple pictures below I hope help clarify how this works.
Yellow handle is the PTO engage lever. It simply pivots forward or back to engage or disengage PTO linkage arm.
Actual PTO linkage arm has the magnet and is shown by the blue arrow.
In normal condition assuming operator in the seat.
When tractor is on/running the magnet is energized (blue arrow) and it attracts PTO lever disk (red arrow).
Move the Yellow handled PTO lever forward and it in turn moves the PTO linkage arm forward to engage the PTO. They are joined via the magnet.
Any safety switch activated and the magnet should de-energize releasing the PTO linkage arm, which returns to the rearward position and disengaging the PTO. Yellow lever will stay in "engaged" position until operator moves it.

"I am a little confused about the zip ties."
The zip ties were used kind of where the yellow line is and went around both the black metal part and the silver one to hold them together bypassing the need for the magnet.

"1. So right now when you flip your added switch to ON, does the dash PTO light come on when you engage the lever?"
Yes. And it also did when the levers were zip tied together. This leads me to believe the PTO light is controlled by the PTO linkage arm which has the magnet on it.
Must be a switch somewhere on the linkage.
"2. If you plug the stock wiring back in, when you move the lever to engage does the PTO light come on if you hold it to engage position?"
I didn't specifically test this but if the PTO linkage arm with the magnet does not move then the light does not come on.
The yellow handled PTO lever does not seem to control the light if the actual arm with the magnet doesn't move to the engaged position.
"3. Somewhere on the linkage you are moving with your hand, there has to be a switch that turns the dash light on and engages the magnet."
The lever with the yellow handle is just that, a lever that pivots forward or backwards.
Nothing else is connected to it other than that disk, red arrow, that is attracted to the magnet when it is energized.
The magnet should be energized at all times the tractor is in normal operating mode.
It should only be de-energized when a safety switch is activated such as the seat or brakes.

Behind the scenes. or below in this case.
The PTO lever, yellow handle, has that metal disk shown by the red arrow.
The PTO linkage arm has the magnet mounted to it. Blue arrow.
Zip tie, yellow line, went around the black part (left in picture) and the silver part (right in picture) at each end of the yellow line to hold them together so when you moved the PTO lever with the yellow handle it would move the PTO linkage arm.

Hope this makes some sense!

wirlybird · Jan 6, 2021

Dave55 said:
Found a wiring diagram.
Everything is in the lower center to left corner.
Looks like there are two 10 amp fuses, top and second fuse that get power from the ignition switch.
Top fuse goes to ignition position on switch.
Power out of fuse goes to PTO indicator light on dash, then goes to PTO Lamp switch and then to hex 1 to complete circuit.
Wish I had a little more detail on the drawing, symbol hex 1, hex 2, hex 3.
I see seven hex 1 symbols, one of which is also labeled engine ground and the one by the ignition switch which appears to be hooked to the ignition switch ground.
I see two hex 2 symbols, with no other marking by any of them.
I see one hex 3 symbol that also has a normal ground symbol by it.
Second fuse is powered from ACC position on key switch.
Power out of that fuse goes to the Operator Seat Switch, if closed then it goes on to PTO selector switch.
From what the drawing is showing if you have the rear PTO only selected, the seat switch and PTO selector switch are the only switches involved to energize the magnet.
If you have mid and rear PTO selected the control module, operator seat switch and the PTO selector switch are all involved.

On a side note, in your first picture in the top left of the picture is that the connector for the magnet?

If so is the right side terminal the positive terminal?

View attachment 2486601

Yes that is the wiring harness side connector for the magnet. The "darker" terminal on the right is positive. I did clean it and can get a good 12v reading at that terminal.

wirlybird · Jan 6, 2021

So now I have actually found some trouble shooting steps for the PTO so I will give that a try at some point to see how it goes and if I can find any answers.
Will report any finding but not sure when I'll get to it.

Dave55 · Jan 6, 2021

So just because the PTO lever is in the engage position, that does not mean the PTO is actually engaged if a safety switch has been tripped.

The only experience I have with a John Deere is my mother and sister both have Zero turn mowers.
If you do not have everything where it is supposed to be, parking brake off, butt on seat, when you try to engage PTO it kills the engine.
My mother used to have a tractor, hydrostatic little one like a 235 if I remember right. If you went to back up you had to hold an over ride if the PTO was engaged or the engine would stop. Butt off seat and engine would stop with PTO engaged. Tractor running and no butt on seat, if parking brake was applied engine would continue running, no parking brake, no butt, engine turns off.

Electro-magnet On PTO Lever Issue

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Dave55

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