# Info on Toro Safety Interlock switch/relay



## AnOldGearhead (Nov 18, 2017)

Grunt said:


> Hey Brother Todd, does that briggs have the notorious interlock module on it? I would like to do a post mortem on one and try to see how they work so new ones could be made once the internal parts are identified. :nerd:



Just wondering, are you referring to the safety interlock levers under the handgrips, or to the limit switch for neutral, or everything? From what I remember the 726 plastic under the levers was a bit different from the later 826 plastic but I don't see a limit switch on the 726 parts diagram...


There's also an stop "interlock" - I hate to call it that - (#297472) on the engine at the governor control plate (#390670) that grounds the magneto when the throttle lever is moved far enough towards slow.


Again, just wondering, thanks.


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## Grunt (Nov 11, 2013)

AnOldGearhead said:


> Just wondering, are you referring to the safety interlock levers under the handgrips, or to the limit switch for neutral, or everything?


 
It is the round cylinder mounted on the lower left side of the motor below the carb that connects the other switches to the mag kill wire. It senses if the auger switch is active or the trans is in gear and kills the motor if the hand grip is released. It is NLA new and used ones are rare and expensive to purchase without knowing if they still work as they should. They can be by-passed which disables the few safety feature there were.


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## Kiss4aFrog (Nov 3, 2013)

:moved: Gave you guys your own thread as hopefully more Toro enthusiasts will see it. 

I think I have one of these on one of my JD blowers but it's resin filled so you can't take it apart to look see. I'll have to go check.
It should just be a relay but cracking open that case would be the way to go to find out.

.


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## UNDERTAKER (Dec 30, 2013)

Grunt said:


> It is the round cylinder mounted on the lower left side of the motor below the carb that connects the other switches to the mag kill wire. It senses if the auger switch is active or the trans is in gear and kills the motor if the hand grip is released. It is NLA new and used ones are rare and expensive to purchase without knowing if they still work as they should. They can be by-passed which disables the few safety feature there were.


* HEY' BROTHER GRUNT!!!!!!!!!! You want that old switch. I still have it??????????*


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## Grunt (Nov 11, 2013)

POWERSHIFT93 said:


> * HEY' BROTHER GRUNT!!!!!!!!!! You want that old switch. I still have it??????????*



Hey Todd, PM sent.


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## Grunt (Nov 11, 2013)

Kiss4aFrog said:


> :moved: Gave you guys your own thread as hopefully more Toro enthusiasts will see it.



Thanks Mark, appreciate it. A relay would need power to operate, so I'm guessing a transistor or a couple diodes will be inside. Opening the case and gentle use of a Dremel should work if different solvents don't dissolve the resin.


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## Mike C. (Jan 28, 2016)

Grunt said:


> Thanks Mark, appreciate it. A relay would need power to operate, so I'm guessing a transistor or a couple diodes will be inside. Opening the case and gentle use of a Dremel should work if different solvents don't dissolve the resin.


Personally,I don't see any need for active components inside that device-no relay is needed.I think it's acting as a terminal or plug block for the connector for the wiring.It's basically the same thing as a lawn tractor safety system for the seat and PTO-no power needed.


I think it acts merely as a way to keep things tidy and wiring the rig at the factory quicker and easier.


Does this blower actually have a relay?I guess that the real question.I've never seen one of these blowers with that safety system,but I can't fathom the need for a relay just to do something as easy as killing the ignition with a few switches.


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## AnOldGearhead (Nov 18, 2017)

Grunt said:


> It is the round cylinder mounted on the lower left side of the motor below the carb that connects the other switches to the mag kill wire.


Thanks, my 826 model #38150 826 doesn't have one nor does the 726 model #31756 that I've seen so I don't know if it was originally on newer or originally was on older machines. I'm guessing that it was added on newer machines after Toro figured out how to use or make a proprietary part, or maybe this whas cheaper than using limit switches. It would be interesting to know the continuity and resistance between the 3 connections...




Kiss4aFrog said:


> Gave you guys your own thread as hopefully more Toro enthusiasts will see it.


Thanks!


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## Grunt (Nov 11, 2013)

AnOldGearhead said:


> Thanks, my 826 model #38150 826 doesn't have one nor does the 726 model #31756 that I've seen



The parts list for the 826 shows the module, the 726 only shows the gear selector safety switch.


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## AnOldGearhead (Nov 18, 2017)

The 826 and 726 machines I had in mind didn't have that. The 826 interlocks work fine but I still need to go through the 726.


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## 351beno (Oct 12, 2017)

Mike C. said:


> Personally,I don't see any need for active components inside that device-no relay is needed.I think it's acting as a terminal or plug block for the connector for the wiring.It's basically the same thing as a lawn tractor safety system for the seat and PTO-no power needed.
> 
> 
> I think it acts merely as a way to keep things tidy and wiring the rig at the factory quicker and easier.
> ...


It does use a small amount of current from the mag that goes to the switches. If current cant return to the module it grounds the mag through the module case to frame.

On snowblowers they used module 41-8600 on 5-8 hp Tecumseh with points, 41-8601 for 5-8 hp tec without points, and module 41-8610 for 8-11 hp with Briggs.


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## dcinma (Dec 13, 2017)

Did you ever find out what is inside these little "cans"?
I recently started a thread for my circa 1979-80 ST724 that uses the same device. The auger safety interlock stopped functioning and I can't figure it out. Ariens calls it a module T and they are hard to find and expensive. Trying to think how I can bypass it and still have the engine shut down if I let go of the right handle bar with the auger engaged.


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## toromike (Aug 20, 2018)

dcinma said:


> . . . Trying to think how I can bypass it and still have the engine shut down if I let go of the right handle bar with the auger engaged.


I've been thinking about alternatives to using the Module T in your machine. I think you can eliminate the Module T if you change to a different kind of switch. I believe that when using the Module T the engine is allowed to run when the switch is closed and the engine is stopped when the switch is open. That's the way the Toro interlock module works. In your thread you stated that the switch is closed when pressed and open when not pressed. The new switch should be the opposite, open when pressed and closed when not pressed (a normally closed switch, NC) because the Module T inverts the operation of the switch and it won't be used. If you remove the old switch and the Module T then replace the old switch with a normally closed momentary switch all you would need to do is connect one terminal of the new switch to ground and the other terminal of the new switch to where the white wire from the old switch cable connected (where the ungrounded side of the key switch also connects). The new switch could be a push button/plunger switch or a micro switch with arm.

I also have some ideas on how to build a substitute interlock module, but that will take some time.


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## dcinma (Dec 13, 2017)

I just realized this was you in this old thread. Thats why I questioned if you guys had actually taken the potting compound to see whats in there.
I just posted the resistance values you asked for on the other thread and a picture.


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## Mike C. (Jan 28, 2016)

toromike said:


> I've been thinking about alternatives to using the Module T in your machine. I think you can eliminate the Module T if you change to a different kind of switch. I believe that when using the Module T the engine is allowed to run when the switch is closed and the engine is stopped when the switch is open. That's the way the Toro interlock module works. In your thread you stated that the switch is closed when pressed and open when not pressed. The new switch should be the opposite, open when pressed and closed when not pressed (a normally closed switch, NC) because the Module T inverts the operation of the switch and it won't be used. If you remove the old switch and the Module T then replace the old switch with a normally closed momentary switch all you would need to do is connect one terminal of the new switch to ground and the other terminal of the new switch to where the white wire from the old switch cable connected (where the ungrounded side of the key switch also connects). The new switch could be a push button/plunger switch or a micro switch with arm.
> 
> I also have some ideas on how to build a substitute interlock module, but that will take some time.


This was kind of the point I was making above-Toro made a very simple system needlessly complex with their mystery module when a few ordinary switches is all that's needed.


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## Grunt (Nov 11, 2013)

dcinma said:


> Did you ever find out what is inside these little "cans"?



I'm still looking for a Toro module to dissect.


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## toromike (Aug 20, 2018)

Mike C. said:


> This was kind of the point I was making above-Toro made a very simple system needlessly complex with their mystery module when a few ordinary switches is all that's needed.


It's more complex than it appears at first. I have thought about why the manufactures decided to use the system they did. I realized that an additional safety feature is provided by using the safety interlock modules. I'm sure these modules contain active and passive electronic components. The modules allow the safety control loop wiring and switch(es) to be supervised. The control loop switch and wiring must be intact to provide the closed loop necessary for the engine to operate normally. When an unsafe condition occurs the loop is opened and the engine will not run. If a wire or switch has been broken the engine will not start and thus the machine can not be used with a safety system that is inoperable. I don't know if there is a statute or regulation that requires that safety control loops be supervised in these types of products. It may be just a matter of minimizing legal liability.

A simple safety switch (one directly wired to the engine coil kill terminal) that is open in the safe operating modes does not provide supervision of the safety control loop. A broken wire could go unnoticed until the operator noticed that the engine did not stop when an unsafe operating mode occurs. A defective unsupervised open loop would allow the machine to be used in an unsafe manner.

However, because of the cost of the modules and poor availability, when a module fails people may chose to disable the safety system completely. I would argue that a safety system that works but is unsupervised is preferable to no safety system at all.


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## JayzAuto1 (Jul 25, 2016)

That Toro system is actually pretty well deigned....And judging by the price, they are VERY PROUD of it. It does work well. I was never able to duplicate the magic in their box... but it's effective and and very necessary, ESP on the Old Toro Snowblowers, that had the levers on top that you had to hold to keep in reverse.... tricky machine to navigate..... easy to let the machine 'Get Away From You'....... If you D/L the Toro Demystify Manual (AWESOME FREE 500 Page Electrical Manual) it explains how it worx. It's very similar to the Ariens Mystery Module of the same vintage. I'v seen some of the Locals swap in an Ariens Module in place of the Toro Module....Successfully, Too!!! Had a few bad Toro cans, nut never found a bad Ariens can.... Coincidence???? IDK. I've never done it, would never do it, BUT in a jamb, EZ enough to do.

GLuck, Jay


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## ST1100A (Feb 7, 2015)

That looks like a "Time Delay" module. John Deere used them on a lot of their equipment and they were nothing but trouble and constant failures with them. Most people had to re-wire everything to by-pass them all-together.
It took a few years for john Deere to realize the constant problems they had with them and the extensive work to bypass them due to the constant failures with them. They finally had to re-do the complete wiring harness and systems to make the machines work again without them.
J.D. did a lot of "Chassis Specific" things so you had to use genuine John Deere replacement parts, any generic "off the shelf" replacement part would not work properly on them.
Other companies started using them for safety switch applications and had nothing but problems with using them in their systems, so a lot of them got rid of using them in their safety systems.


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