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Clue me in on this one. Having "no idea"? FYI voltage is induced by magnet attached to flywheel. Where does electrical energy come from, to activate blade clutch, if it isn't from the energy created by the magneto? With no battery, no alternator? Pull start motor only.
FYI: Voltage does not come from the ignition magneto on that engine. It has an alternator even though it is pull start. Something I would have thought that you would know and understand in order to conduct electrical tests on it. Now knowing you did not know that, I question whether you were conducting tests correctly.


Just so you know, a magneto DOES create voltage, technically it supplies pulses of high voltage. Other electronic parts in the circuit are using that magneto voltage to supply current to the electric clutch so it can move the blades. The original Briggs points-style magnetos had about 6 -8 volts on the primary when pulling the starter rope and around 300 - 400 volts on primary when actually running.
Just so you know, I know what a magneto is and how it works. Yes, it supplies electrical pulses. That's it. It fires the spark plug. It DOES NOT create electricity for use in the rest of the wiring system. It's ONLY function is ignition/spark. I know all about point ignition and magneto ignition. Don't need any explanation.


the electric PTO, I never stated anything about an "engagement" motor, Also I never used the word "solenoid" in any of my original threads here. You're projecting words on me, which I never stated.
That is correct, YOU did not. If you read, I was quoting brian.joe.kelly, not you. (eye roll)


Yeah, I agree that "safety interlock system isn't working correctly". That statement and 99 cents might get you a cup of coffee. Although all comments are appreciated, yours are no better than any of the other posts, basically which are as good as a needle in a haystack right now. I'll let the Scag mechanic confirm that I have a bad wiring harness somewhere. I'll let you know what the professional Scag mechanics find out for me this week. I'm 95% confident that I've already ruled out neutral switches and PTO switch at this point, so far spending about $100 in parts that I didn't actually need but sometimes you get lucky with the shotgun approach.
Again.... I was quoting brian.joe.kelly, not you.
I'm glad you took it to a "professional Scag mechanic". After giving a bit of thought to this whole deal, I bet you find out that you have/had a bad Regulator/Rectifier on the motor. Trying to solve an electrical issue over the internet for someone else is ALWAYS a "needle in a haystack". I don't know why people think it would be anything other than that. I literally can't see your machine, or conduct tests on it, and I have no idea if you are conducting the tests properly. I don't even know for sure 100% that the information you are giving is true. If you conducted a test improperly, then report information back to us, it is true information to YOU, but not actually true since the test was not conducted properly. I think it is just awesome you finally took it to a professional. Let us know what they find.


And if you are going to harp on someone about something they said, make sure they were actually talking to you, as in quoting you, not someone else. A "shotgun" approach is NEVER the way to solve a problem. Yep.... sometimes you get lucky. Most of the time you just waste your time and create even more problems replacing components that were not bad. Problem is compounded if you bought parts via the internet and not at the dealer, because in the case of electrical parts, particularly safety switches, you may receive the wrong part. Two different seat switches for example can look exactly the same, except one is a N/O and one a N/C switch. But by visual inspection they are exactly the same. Only when you test the switch with a DVOM do you find that is is incorrect. And that is only if you know the difference between the two types of switches and know which one your machine actually uses. It's a sh!t show trying to diagnose electrical issue online.
 

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Wow. You have absolutely no idea what you’re talking about. Why are you trying to help?

A magneto doesn’t supply any voltage to the electrical system whatsoever.
An electric PTO does not have an engagement motor.
An electric switch is just a contact switch, not a solenoid.
The reason the engine is dying is because the safety interlock system isn’t working correctly. There is no problem with the PTO. The safety interlock kills the engine if proper conditions are not met. That’s the system that isn’t working.

Duuuuuude. Wow. Just stop. 😵😵
"Duuuude Woooow"
You've seen by now the original poster convincingly tell you that a magneto supplies current (charge) and voltage (pressure).
Ok, it's not an "engagement motor" and the switch is not " a solenoid". Big deal.
Electricity goes through the pto switch down to the clutch assembly to move it into engagement- likely. What does that but some kind of motor converting electrical energy to mechanical energy? Similarly, a solenoid is an electrical switch that needs electrical energy to induce mechanical movement to operate the switch. It's not far flung. But it sounds like it's a simpler mechanical switch.

But all that's all beside the point
The troubleshooting creative thinking and ideas are the point.
He has a short likely after the switch- between the pto switch and the clutches.
I suggested that he might catch a short with an ohmeter, the engine off, and turning the pto switch on. The "solenoid" that grabbed your attention, was an after-thought that the pto switch itself might need power to operate- like a "soft touch switch". Again, who cares about the switch. It's primarily the thinking of isolating the wire branches of his magneto power..

"Duuuuude" do you get why it's not a short likely between the magneto tap and the current input side of the switch, "Duuuuude"?

"Duuuuude" why stop now??? You knew so much to tear me down, I mean you were just on the cusp of something brilliantly instructive. You're the best, "duuuuude". That's what smart people do, everywhere, every-time throughout humanity, put other people down, and offer no workable, instructive answer? Or is it a self-esteem problem? I forget.

"Duuuuuude", Am I taking it a little personally?
 

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"Duuuude Woooow"
You've seen by now the original poster convincingly tell you that a magneto supplies current (charge) and voltage (pressure).
Ok, it's not an "engagement motor" and the switch is not " a solenoid". Big deal.
Electricity goes through the pto switch down to the clutch assembly to move it into engagement- likely. What does that but some kind of motor converting electrical energy to mechanical energy? Similarly, a solenoid is an electrical switch that needs electrical energy to induce mechanical movement to operate the switch. It's not far flung. But it sounds like it's a simpler mechanical switch.

But all that's all beside the point
The troubleshooting creative thinking and ideas are the point.
He has a short likely after the switch- between the pto switch and the clutches.
I suggested that he might catch a short with an ohmeter, the engine off, and turning the pto switch on. The "solenoid" that grabbed your attention, was an after-thought that the pto switch itself might need power to operate- like a "soft touch switch". Again, who cares about the switch. It's primarily the thinking of isolating the wire branches of his magneto power..

"Duuuuude" do you get why it's not a short likely between the magneto tap and the current input side of the switch, "Duuuuude"?

"Duuuuude" why stop now??? You knew so much to tear me down, I mean you were just on the cusp of something brilliantly instructive. You're the best, "duuuuude". That's what smart people do, everywhere, every-time throughout humanity, put other people down, and offer no workable, instructive answer? Or is it a self-esteem problem? I forget.

"Duuuuuude", Am I taking it a little personally?

You better read the reply I made just before your post. You two neither one understand how this system works whatsoever. I don't have the time to do electronics 101 with either of you. We are just going to have to agree to disagree, or at the very least you need to accept you just really don't know what you are talking about, and there are people who do, "dude".
 

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You better read the reply I made just before your post. You two neither one understand how this system works whatsoever. I don't have the time to do electronics 101 with either of you. We are just going to have to agree to disagree, or at the very least you need to accept you just really don't know what you are talking about, and there are people who do, "dude".
You think the original poster doesn't know after installing the engine, does it have an alternator or not?
To be fair, to you, maybe it's possible. Unlikely, from how he's described things.
I was offering some thought process that might be helpful. Nothing else.
So in your philosophy, apparently, unless you bluster as a know it all, specific this, specific that, what you have to say is useless, and shut up- duuude, Have I got that right?
We agree that electrical problems are tricky by nature.
He's fairly advanced both in general and in his particular problem. But rightfully, he thought someone out there might have dealt with a very, very similar problem with a similar model Scag, perhaps gone to the Scag dealer, found out it was XYZ, etc.
 

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Discussion Starter · #25 ·
You think the original poster doesn't know after installing the engine, does it have an alternator or not?
To be fair, to you, maybe it's possible. Unlikely, from how he's described things.
I was offering some thought process that might be helpful. Nothing else.
So in your philosophy, apparently, unless you bluster as a know it all, specific this, specific that, what you have to say is useless, and shut up- duuude, Have I got that right?
We agree that electrical problems are tricky by nature.
He's fairly advanced both in general and in his particular problem. But rightfully, he thought someone out there might have dealt with a very, very similar problem with a similar model Scag, perhaps gone to the Scag dealer, found out it was XYZ, etc.
All useful comments are carefully examined by yours truly. FYI I just looked at one the Scag WB manual pull start electrical diagrams.
16HP BV (Briggs Vanguard) engine.
Rectangle Font Parallel Diagram Art

I don't have an hour meter on this mower so those wires remain unused. Definitely don't see any kind of alternator/stator wiring as someone has suggested so it's not there to produce current to blade clutch. I assumed magneto is producing the current to operate blade clutch given some power diodes/rectifiers to smooth out the sine wave.

Mechanics have mower at shop, but work backload is at least a week or two...
 

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Definitely don't see any kind of alternator/stator wiring as someone has suggested so it's not there to produce current to blade clutch. I assumed magneto is producing the current to operate blade clutch given some power diodes/rectifiers to smooth out the sine wave.
That is incorrect. Alternator is under the flywheel like any other Vanguard. There is a R/R on the side of the engine last one I looked at. It would be in the manual for the engine. You CANNOT run electrical components off the ignition magneto. Guys....... it doesn't work that way. I don't care if you don't believe it or even understand. It has to have a stator to make the necessary voltage.
 

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Are the amps produced by the engine enough to power the clutch? IE engine produces 15amps the clutch needs 20+? (True question....)
 

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Discussion Starter · #28 · (Edited)
That is incorrect. Alternator is under the flywheel like any other Vanguard. There is a R/R on the side of the engine last one I looked at. It would be in the manual for the engine. You CANNOT run electrical components off the ignition magneto. Guys....... it doesn't work that way. I don't care if you don't believe it or even understand. It has to have a stator to make the necessary voltage.
Since I have a pull start mower and don't have a battery, starter or headlights on this WB mower, are you saying that there is a stator with magnets on underside of flywheel to energize blade clutch?f If so, that might zero in on problem. Bad wiring from stator to PTO circuit.

My Vanguard engine manual doesn't appear have anything with a diagram and layout for blade clutch, but does show a stator/alternator under flywheel.
 

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Since I have a pull start mower and don't have a battery, starter or headlights on this WB mower, are you saying that there is a stator with magnets on underside of flywheel to energize blade clutch?f If so, that might zero in on problem. Bad wiring from stator to PTO circuit.

My Vanguard engine manual doesn't appear have anything with a diagram and layout for blade clutch, but does show a stator/alternator under flywheel.
Yes, now you understand
 

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Discussion Starter · #31 · (Edited)
Yes, now you understand
Thanks for the info, I’ll await confirmation of this possible problem as soon as local Scag mechanic can run tests on my WB 48in mower.

Will probably be pulling off flywheel to replace stator this time, unless shop rates are within my budget.

OTOH I would not have guessed that any flywheel components would have went bad so soon after brand new Vanguard engine was installed, it came complete without a muffler, which I yanked off old engine and used it on new motor.
 

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Since I have a pull start mower and don't have a battery, starter or headlights on this WB mower, are you saying that there is a stator with magnets on underside of flywheel to energize blade clutch?f

This might help.........
 

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Thanks for the info, I’ll await confirmation of this possible problem as soon as local Scag mechanic can run tests on my WB 48in mower.

Will probably be pulling off flywheel to replace stator this time, unless shop rates are within my budget.

OTOH I would not have guessed that any flywheel components would have went bad so soon after brand new Vanguard engine was installed, it came complete without a muffler, which I yanked off old engine and used it on new motor.
Please don’t go “yankin” parts. You can test the stator and R/R to see if it is indeed working. I am not saying I think it’s bad. You could simply have lost ground to the R/R and so it isn’t working. I highly doubt the stator failed. They almost never fail.
 

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Can get in the dustup? The switches on the brake, presence lever, pto have terminals that depending on the position of the switch OPEN or GROUND the terminal on the blower housing this terminal goes under the shroud to the magnetos. When the switches are in the proper position they open the path to ground ie brake on, pto switch off. when the engine is started The brake terminals close, with operator presence levers held down the circuit is again opened by those switch or switches, now unit is able to be self propelled, Operator presence levers released grounds the magnetos and kills the engine. The same applies to the PTO switch, Brake, off - OP held down - PTO switch off ground is open--PTO switch on brake off, OP held down engine should run. IF it shuts off there is a problem with one of these switches that grounds the magnetos.
Using an OHM meter test the switches to find the bad one. Be sure when the OP lever is held down the switch is activated, something may have slipped or been bent.
If you have a wiring diagram (operator manual or on line?) It helps you to know what color wire you are looking for.
NOTE all of this has NOTHING to do with the alternator or clutch. This is an issue in the machine NOT the engine.
Unless you have a bad clutch bearing or a problem with a spindle, or idler. If that was a problem removing the belt would "prove" the problem.
By the way a quick check-- Remove the shutdown wire from the terminal on the shroud and see if it still stalls That wire is on a stud on the right side of the engine usually a spade terminal. If it runs you have confirmed a bad switch or a shorted wire.
 

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Discussion Starter · #35 ·
Scag mechanic has already diagnosed my problem, mower is ready to be picked up. Couldn't follow what the sales cashier said, I heard him say something about the plastic tab connector for the blade clutch, but he wasn't following too much of all what was written down by the mechanic. I didn't have time to pick up repaired mower today, just paid the $56.00 total bill from the mower shop. Monday morning quarterbacks would say I should taken it to the shop before I put all the new switches on mower. Yeah, and I'll look over the mechanic's note tomorrow.
 

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Discussion Starter · #36 ·
Scag mechanic has already diagnosed my problem, mower is ready to be picked up. Couldn't follow what the sales cashier said, I heard him say something about the plastic tab connector for the blade clutch, but he wasn't following too much of all what was written down by the mechanic. I didn't have time to pick up repaired mower today, just paid the $56.00 total bill from the mower shop. Monday morning quarterbacks would say I should taken it to the shop before I put all the new switches on mower. Yeah, and I'll look over the mechanic's note tomorrow.

Mechanic told me that the problem was with the plastic operator presence switch, actually a small tab on the plastic switch that was interfering with its range of motion, preventing the circuit from connecting current from PTO toggle switch and to electric clutch to turn the belt that runs the 3 spindles and blades.
Wood Motor vehicle Vehicle Automotive exterior Gas


It's the one I didn't replace, it's hidden under the mower's front faceplate which has the operator PTO toggle switch and key switch. It's controlled by the handles on each side of mower. I have a short video clip of the underside of faceplace to show plunger and spring operation when operator control handles are used.
 

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Monday morning quarterbacks would say I should taken it to the shop before I put all the new switches on mower. Yeah, and I'll look over the mechanic's note tomorrow.
I don’t follow sports...,.
but maybe you learned something from this incident? Down time costs more money than a repair bill in most instances.
 
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