1992 Craftsman Riding Mower Dies When Blades Engaged, Safety Switch Issue

[Blaine B.]

This is a perplexing issue considering that I didn't have any problems with this last year.

In October of 2018 I bought a 1992 Craftsman 36" riding lawn mower. Shortly thereafter I disabled the seat safety switch, simply by unplugging it since the circuit is only closed when the seat switch is not depressed. When someone is sitting, the circuit opens, so simply unplugging the switch results in an open circuit. No issues!

This past Wednesday was the first cut of the year, which is the first time I experienced this issue. Nothing has changed with the lawn mower with the exception of the battery being disconnected all winter, and being low and needing a boost because I had neglected to check the charge ahead of time.

This lawn mower has 3 safety switches as far as I can tell, and since the lawn mower is from 1992, the technology is relatively primitive. There is the 2-wire seat safety switch, a 2-wire brake/clutch safety switch, and a 5-wire, 4-prong PTO/deck engagement safety switch.

Both the brake/clutch safety switch and PTO/deck engagement safety switch are unmodified, still connected, without any "green crusties" in the connections.

I can start the lawn mower normally so as long as my foot is depressing the brake/clutch and the PTO/deck is off. However, as soon as I just ever so slightly move the PTO/deck engagement lever, the mower cuts off.

What am I missing here? Obviously it's as if there is a safety switch tripping out, but why? I didn't have any issues at all throughout the entirety of last year's lawn mowing season.

I was still able to cut Wednesday by jumping the starter, which apparently bypasses all of the mower's electronics including all of the safety switches and the keyed ignition switch too. Being 1992 technology, when you jump the starter, it will run as long as it has fuel, air, and spark, regardless of which position the ignition switch is in. So, that'll be my method until I figure this out!

I'm perplexed because the system is so simple, but I must be missing something! It can't be the seat safety switch because having it be disconnected leaves the circuit open which is normally what state it is in when it detects weight on the seat.

What should I check next? This afternoon I tinkered around with it a little more and couldn't find what is causing the issue. No rat or mice chewing. Nothing has changed except sitting in the garage for the winter.

 

[bertsmobile1]

A couple of tings come to mind but need to know a little more about the mower.
Does it have a manual or electric PTO ?
IT sound like you have a manual one but that should only have a 4 terminal PTO switch.
Secondly the magneto is grounded by the key switch so if the key is off then the engine should not run at all due to no spark.
And yes jumping directly to the starter bypasses the safety switches in the cranking circuit.
I gather it predates carburettor fuel shut of solenoids as well .

I know it is an old mower but posting the craftsman model number would be a great help as it could have been made by AYP, Murray, or MTD or perhaps even Noma, can't remember what year they went under.

 

[Blaine B.]

Hello, it has a manual PTO, lever actuated. It also does have a 4 terminal PTO safety switch but I believe there are 5 wires - from what I remember there are 2 black wires that go to one of the 4 terminals.

If the magneto is grounded by the key switch, why did the ignition switch have no effect last Wednesday after I jumped the starter? I literally took the key out and it still ran. As far as I know the ignition switch is OK, it starts, runs, and cuts off normally otherwise if started by the key switch. I removed the ignition switch yesterday and used my meter to test the contacts. Also cleaned it out with electric contact cleaner. Seemed to be showing proper continuity when turned in the proper positions.

It seems to me that the mower is receiving some sort of safety signal that dictates the motor to turn off when the blades are engaged, just as it normally should if it was not sensing an occupant sitting on the seat. However, that safety switch is unplugged! The reason I unplugged it is that the entire lawn mower would shut off if you stepped off. I suppose to stop the mower from running away if it was left in gear. So that aspect still works as I intended by disconnecting the seat safety switch, as you can start the mower and leave it running without having to sit on it anymore. It's just the blade engagement that kills it now. And it's definitely due to the safety switch, not a seized pulley or belt. Everything works fine if it's jumped out.

It's just unusual that these issues pop up after sitting all winter. I suppose it's possible the ignition switch has the "green crusties" internally as I do rinse my mower off after each use, but wouldn't some other unexpected electrical issue present itself as well? Everything else seems normal.

From the sticker on the body, the model number is 917.256820. I believe it was manufactured by AYP as I learned when I created a little thread when I bought it in late 2018.

 

[bertsmobile1]

OK
The terminal with the double black wire is the seat switch.
Check each of the terminals for ground.
They all should be open circuit to ground
If not you have a short somewhere .
And I would be betting it is around the seat switch wires.

On the back of the key switch will be the letters.
B=battery
G=ground
M=magneto
S=starter
A= alternator
L = lights
There might be others but they are not important.
Check that you have got ground on the G plug terminal
And that the switch connects G to M in the off position ( grounds magneto)_, then check that the kill wire is also showing ground when you turn the key switch off.
In the meatime I will try to dig up your wiring schematic .

Your mower is around the age when wires work harden and break where the crimp terminal joins the wire so give them all a litle tug when you check them.

 

[Blaine B.]

I'll check on this later today. I know that the ignition switch has to ground the magneto because it turns off normally. It just had zero effect on Wednesday when I jumped the stater after running into these "new" difficulties. I played with it more yesterday to understand what was going on but on Wednesday I was a bit in a rush to start as there was rain coming later in the afternoon.

None of the wires seem to be brittle actually. The mower is in incredibly good shape for its 28 year age. Very surprisingly so actually. I posted pictures awhile back but now the forum layout is different and it's saying they are too large. I don't feel like resizing at the moment. It was obvious to me that this mower was never stored outdoors and was a steal for the $180-$200 or so I paid for it I felt.

If you're interested to take a look, I uploaded this video quite awhile ago, shortly after I got it:

 

[bertsmobile1]

Thanks,
I saw the original post/
hard to find information on it as it is from the pre-Husqvarna AYP days.
The same mower was sold down here painted green & badged Electroluxe
And yes the Engine is worth that alone.
The wires do not go brittle for their full length just where the terminal is crimped on
When I do a crimp I put 2 pieces of heat shrink of different lengths over the crimp & wire to support the wire to prevent this happening.

 

[Blaine B.]

I didn't end up doing anything with it today. Maybe Monday! I might just go through the harness and see what I can remove and simplify. I honestly don't need any of these safety switches any longer, and the need to keep it "stock" isn't really necessary any longer.

Do you think it's ignition switch related, is there any way possible? Since the switch sits horizontally and these keys do not have that shield like some of the newer keys. Every time I rinse the mower I wonder if water gets down in there. That could really be the only thing that would have had time to sit and "fester" all winter long. But like I said everything with the key appears to work. Start, run, and stop all functions properly. And I don't have any lights so no testing there.

If you watched the video and heard that loud metallic clanking/banging sound when choked and running at low idle, that turned out to be the crank pulley being loose. It wasn't fully seated and was bouncing up and down I believe. Once I found that and torqued the crank pulley bolt that noise disappeared! Heck, maybe that's why the guy sold it. He hadn't mentioned it but I wonder if he thought it had a rod knock that came and went. Just speculation after the fact! For quite some time I couldn't figure out what it was. But the pulley was so loose it probably had an inch of lateral travel on the crankshaft.

 

[Cusser]

I know my 2005 42" mower will die in reverse with the blades engaged with key at the "normal" run position (mine also has a separate key position to allow reverse mowing). Does your ignition switch have similar feature? If so, worth investigating.

 

[Blaine B.]

I know my 2005 42" mower will die in reverse with the blades engaged with key at the "normal" run position (mine also has a separate key position to allow reverse mowing). Does your ignition switch have similar feature? If so, worth investigating.

As far as I know this older mower does not have that feature. I think that's another safety added to newer mowers to make you think before reversing with the blades engaged. There are no extra buttons or key positions between off, run, and start.

 

[Blaine B.]

Consider this problem rectified.

I'm not sure what the problem was as all of the safety switch wiring was in pristine condition, nothing brittle, no broken connectors, etc. So, I simply removed all 3 of the safety switches and all associated wiring, and joined a couple of the wires that had to be cut. So everything works fantastic once again without ever having to worry about a safety switch issue. Considering that no one else uses this riding mower besides myself, having the safeties eliminated is not much of a concern.

It is strange that this issue would present itself after sitting for a winter, but regardless, it won't have to be thought of any more.