Craftsman safety switch troubleshooting

baymee(LehighValleyPA)September 20, 2009

I went to a friend's house to look at a no-start condition. He told me that he adjusted his clutch rod all the way and then it wouldn't start anymore, so I looked at the clutch safety switch.

I never had to electrically troubleshoot the safety circuit before, so I really didn't know how it worked, but eventually we got it running.

I found a link to the Craftsman wiring on this site and I'd like to know a few things about the switches for the future.

The clutch/brake switch appears to be: On depression, the white contacts make and the black contacts break, allowing power to go the PTO in the OFF position and on to the solenoid.

The seat switch is more confusing. It appears to operate on the ground wire and in the unoccupied position, grounds out the ignition.

My question is: How does the seat switch in this diagram work? If the top contacts are made, seat unoccupied, the ignition is grounded out. The bottom contacts are broken in the unoccupied position which doesn't make sense to me. If they closed, the ignition would be grounded and if they stayed open, there would be no need for them.

Any help appreciated.

Here is a link that might be useful: Craftsman 917.251490 wiring diagram

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How about a graphic explanation for the masses?
The diagram does not explain in text, but you must infer that the center horizontal band of the switch illustration is when the seat is occupied. Top band = Seat vacant. Bottom band = Switch connector unplugged. It is a "shorting" or Grounding connector.

    Bookmark   September 20, 2009 at 12:43PM
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Still clear as mud.

I can understand the top two positions but how are the bottom two contactors affected? Pressure from the weight on the seat wouldn't pull up the bottom contactor.

As I read the print, the ground circuit kills the ignition. It doesn't complete a circuit as a normal ground would.

    Bookmark   September 20, 2009 at 5:10PM
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I'll give you my opinion That should clear it right up!?!?? Ha, Ha.

the switch is either "on" or "off" switch just like a light switch in your house???????. when it's off, no ignition when you butt is "not" in the seat providing the switch is working right. and when "on" completing the circuit or (gounding out the circuit depending on what the switch is suspose to do) which allows the ignition to fire with your "butt in the seat" "switch on". this is why these switches can easily be bypassed with a jumper wire.

    Bookmark   September 20, 2009 at 5:21PM
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***"this is why these switches can easily be bypassed with a jumper wire."***
Wrongo! Incorrecto!
Jumpering anything in this switch or connector will only provide a double dose of what the switch, and the connector contacts, are designed to do. Seat switch contacts A & B in the illustration below are inside the switch body. Contacts C & D are in the body of the electrical connector that "connects" to the switch. The contact strip serving contacts C & D is moved to the open position by a plastic "riser tab" in the seat switch body whenever the connector is plugged in to the seat switch. When C & D are not in touch with each other via the contact strip, that portion of the circuitry is disabled, or "inert". When C & D are inert, they cannot ground the engine ignition.....engine is permitted to run, if the seat switch itself has been satisfied. When the connector is unplugged from the seat switch, contacts C & D are joined by the contact strip, and the engine ignition becomes grounded.......engine dies.
The functions of the seat switch itself operate to affect the exact same circuit as the seat switch connector. In fact you could describe this as two separate, independently operating switches, one in the switch body, and the other in the connector body.

    Bookmark   September 20, 2009 at 8:53PM
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I think it finally sank in. That was a good explanation.

Like I said, I never ran into a safety switch problem before and they seem to be pretty reliable, but it's good to know.

    Bookmark   September 21, 2009 at 6:29AM
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wrongo I have to agree but,So you just need two or three jumpers for that double switch, again provide you know what the switch does in each mode.

I see these switches jumped from time to time and when you buy used you NEVER know what your going to get. Lets face it people are either too lazy or too cheap to repair a cheap switch that all it does is make contact. The bad part is and I agree if bypassed the safety function it provides is "gone" and Some will cut the wires and just wrap them togather.

Luckily Most do not understand elect device, understand the use of a multimeter, or have the knowledge to deactivate it as we have seen by the low precentage posts the pop up "HOW DO I Disconnect my RIO switch" . Right or wrong it happens all the time. Something you need to be aware of when buying used LT from Newpapers (about to be the thing of the pass) or online adds.

That's why when somebody buys used and want's the tractor to function properly at the time of it's manufacture it's best to test these functions so when you need them they are there to protect you. MTD or AYP products seems to be on the cheesey end of switch design and function so naturally they have most of the problems

    Bookmark   September 21, 2009 at 9:23AM
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rc, in the seat switch configuration featured in this kind or number of jumper wires will defeat the "kill engine" effect. Adding a jumper wire or wires to THIS arrangement is like cutting the wire connector off with a wire cutter and then "butt splicing" the wires together, and that will ground the ignition circuit, resulting in "no spark-no run". Realistically, there may be some OEM configurations of the seat switch that have 12VDC run through them that control a relay (wherein the relay grounds the ignition circuit to kill engine) but I have not encountered any of those (yet). I ain't disputing you that some operator presence switch circuits can be defeated by jumpering, but the set up used by Craftsman in this case is not one that can be defeated with jumpers. Clutch/brake switches are a different story. Some of them ARE configured to control 12VDC (in the starter control interlock circuit), and are therefore vulnerable to "jumper wire monkey business". Some of them are "dual function" and tied in with the operator presence circuit to kill engine if seat is vacated without the clutch/brake pedal locked on.

    Bookmark   September 21, 2009 at 12:12PM
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the ones I have encounter must be older designs. The three mowers I have from the 80's, 90's, and early 2000's all have two wire seat switches. This includes three manufactures. AYP Craftman, MTD Cub Cadet, and JD LX.

    Bookmark   September 21, 2009 at 1:22PM
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john9001(SW, PA, 6)

just came across this problem today, my seat switch tests ok but the "grounding plug" is bad and that plug looks to be part of the main harness with no part number. I do not want to replace the whole harness.

any ideas?

    Bookmark   July 13, 2014 at 2:13PM
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I can't see what would be wrong to snap out the plastic tab and spring in the connector. That is as long as the connector is attached to the seat switch, it will work as it should.

    Bookmark   July 13, 2014 at 3:40PM
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***"the grounding plug is bad"*** As in broken plastic connector, or what?
You only have a couple of options when this happens.
You might try to find a used one off of a scrapped out chassis at a small engine shop.
Or, you can cut the one piece connector off of your harness and replace it with 2 individual, insulated female spade connectors.
The only thing you will lose is automatic shut down if one of the individual connectors should come off of the switch. The switch will still function to shut off the engine if you rise off the seat in an unsafe manner, or if you otherwise vacate the seat without the parking brake being set.

    Bookmark   July 13, 2014 at 3:57PM
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john9001(SW, PA, 6)

Thanks, I have decided to remove the spade connectors from the grounding plug and plug them directly into the seat switch. At least until I can find another grounding plug.


    Bookmark   July 14, 2014 at 9:42AM
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