Corrections to my 416-H Safety Interlock System

[rmaynard 14,951]

NOTE: The wiring diagrams in both the manual and in the electrical demystification guide are INCORRECT. All diagrams shown here have been corrected to the best of my knowledge.

 

According to the owner’s manual, the 1996 416-H is supposed to have the following Safety Interlock System.  It is designed to prevent the engine from starting unless:

• You are sitting in the seat
• The brake pedal is depressed
• The PTO is OFF
• The speed control lever is in neutral

However, that scenario is not possible as the 416-H is wired.

• You DO NOT have to be in the seat
• Depressing the brake pedal is NOT necessary
• The PTO does have to be off
• The speed control lever is in neutral

Two out of four is not a good safety record, and the two that are correct are in the START circuit, not the SPARK circuit.

 

Here is why the Safety Interlock System is faulty.

 

Seated on the tractor, the key is turned to the RUN position, and the seat switch being closed by the operator’s weight, activate the SEAT RELAY, closing the normally open contacts within that relay.  This completes a path for 12 volts to flow from the RUN position on the ignition switch to the (+) side of the coil. So now we have SPARK.

 

 

However, if you lift up off the seat switch, which should prevent SPARK and therefore not allow the engine to start, the path of the 12 volts changes as the seat relay de-energizes and the contact returns to the normally closed side, creating a path as shown in the next picture.

 

 

So this is the first problem. This allows the operator to start the tractor while not in the seat, and worst yet, will cause the tractor to keep running if the operator should fall from the seat while moving, hense the term "deadman switch". However, another wrinkle is that if the PTO is engaged, as in mowing, the seat switch functions properly and will kill the engine if the operator lifts off the seat.

 

THE CAUSE:

 

There are two PTO switches. The first one (shown in the diagram above) is supposed to function to create a "kill" scenario when it is engaged, which it does, but it also creates an incorrect path when not engaged. The second PTO switch prevents the START circuit, keeping the starter from turning if engaged. That one works correctly.

 

MY DILEMA::

 

I want the best of both worlds. I want the seat switch to function properly so that if someone is operating the tractor and falls from the seat, it will stop. Also, I want to be able to start the tractor, get off the seat and let it run (great for those cold times when the hydro needs to warm up). I also want a way to start the tractor while not in the seat, for service, etc.

 

MY SOLUTION:

 

Here is how I modified my 416-H to correct all the above. I added a second PARKING BRAKE SWITCH. Look at the diagram below.

 

 

When the parking brake is set, the second switch is closed completing a circuit through the PTO switch allowing me to start the tractor while not in the seat. In this condition, the brake is locked, and the motion control is in neutral.

 

When the parking brake is released, the switch opens. This open the circuit that was running through the PTO switch, and now causes the engine to stop if I lift off the seat.

 

NOTE: The owners manual says that with the parking brake set, the engine should not crank. However, setting the parking brake has nothing to do with preventing the engine from cranking. The parking brake switch's only function is to turn the light on or off on the dash.

 

Okay, did I over-think this, or is it a viable fix?

 

 

 

 

 

 

Edited February 12, 2015 by rmaynard

[bmsgaffer 2,043]

Best as I can tell without trying it myself, the theory looks sound.

 

That's very safe, but you can never put the tractor on a trailer without being in the seat would be my only issue... But that may not be a big issue for ya.

[rmaynard 14,951]

That's very safe, but you can never put the tractor on a trailer without being in the seat would be my only issue... But that may not be a big issue for ya.

 

You've got a good point. You see two heads are always better than one.

[bmsgaffer 2,043]

If you like the dead man switch idea (I know I do) maybe mount a small toggle switch under the hood and have Terry rig up a nice label for a 'parkbrake-seat switch override' that would bypass your parking brake switch addition...

 

You wont need that 'mode' very much but at least you will have the ability to turn it off when loading/unloading.

Edited February 12, 2015 by bmsgaffer

[doc724 924]

Thx, Bob,

 

If I ever get a 416H (looking around now), I will be sure to keep this in mind.  On the newer machines, there are so many interlocks/switches (for example, on 8 speeds, must be in neutral, on a hydro must have the parking brake on), that many times, I go out, turn the key and nothing happens.  After a couple of "aw s..t, a dead battery"  I remember to look around for the obvious.

[rmaynard 14,951]

What I don't understand is how the interlocks are all different from model to model. On the 416-H (at least my 1996) it seems strange that as manufactured, the seat switch is not a deadman. That is why I am modifying the entire circuit. I have four grandsons that are getting old enough to drive the thing, and I don't want them on it without a working deadman switch.

[buckrancher 2,678]

the seat switch should only work when the mower is engaged what you need is a kill switch like on a boat or snowmobile that is hooked to the operator so if he falls off the motor will stop

 

 

Brian

[bmsgaffer 2,043]

You can modify the seat switch circuit to be a deadman switch with an extra switch on the parking brake and some basic wiring. The newer tractors generally have it this way, and that's what Bob is working on.

 

Should be a pretty safe old tractor after hes done

[rmaynard 14,951]

 That's kind of like my 93 year old aunt in a nursing home. She had a wire clipped to her clothes, and the other end to an alarm on her bed, or chair. If she got out of her bed or chair, the alarm would go off. She was smart enough to just unclip it, and go where she wanted, mostly to the employee snack machine. Kind of like bypassing the seat safety switch.

[Martin 2,130]

What I don't understand is how the interlocks are all different from model to model. On the 416-H (at least my 1996) it seems strange that as manufactured, the seat switch is not a deadman. That is why I am modifying the entire circuit. I have four grandsons that are getting old enough to drive the thing, and I don't want them on it without a working deadman switch.

 

Bob, could this be also called a Commando switch?

 

You would have to know in advance when those particular 'Commando' situations could be about to happen and flip the switch before hand, you know, just in case something happens........ 

Edited February 17, 2015 by Martin

[Martin 2,130]

Im sorry Bob, thought just popped into my head when i glanced at your sig just then.......

Edited February 17, 2015 by Martin

[rmaynard 14,951]

Martin, I am literally laughing my butt off. When I get Terry to make me a custom decal, I think I will call it the" Commando Switch".