Testing Toro safety system module

I have a 1987 Toro 832 rider model 56125 that started acting up (Shutting down the engine when engaging either the transmission shift lever or the mower deck engagement lever. Pulling the module PN 54-7920 out of the harness will allow me to engage either or both levers and keep running (although somewhat unsafely) I have tested each safety switch independently for continuity, or unwanted grounds, and all are functioning like they should. What I don't have is a test procedure for the module to verify that it is the culprit. It will be an expensive lesson if using a new one is the only way to test my conclusion!

 

As far as I know.... all three switches need to be closed/shorted which keeps the relay open in the module so that it doesn't supply a short to ground on the magneto line.

So........
green to brown needs to be 0 volts if key on or 0 ohms (shorted) if checked with key off.
yellow to brown needs to be 0 volts if key on or 0 ohms (shorted) if checked with key off.

The module is pretty inexpensive so there isn't much more than a relay and a couple of diodes inside it.

 

Pete, can I assume that your Green to brown, and yellow to brown needing to be O ohms would apply if the module is out of the tractor and no power line supplied to it? On your diagram and one of mine, it also shows the switches being normally closed. this mower has always been able to start and run WITHOUT me sitting on the sear, even though the seat switch tested as working with a continuity tester. With everything hooked up, and the engine running, me sitting on the seat (or not) engaging either the trans lever or the deck engagement lever would instantly kill the engine. Does that make the Module sound like the "smoking gun to you? I quick ran a test with an ohm meter on the module. Both had 2 plus ohms between the wire colors you mentioned, not zero.

 

I can't tell you what the wires on the module measure.
I can only tell you what needs to happen for it to work.

Any switch not closed will keep the spark shunted.

 

The new module came today after my last post. I quickly ran the same check on the same contacts you menttioned and had O ohms between them. Before I install the new module, do you have any suggestions as to what else I should check that might have fried the last one? It was more like 3 Ohms between the contacts than 2.

 

Trans - deck - seat. Three switches.
I don't own tractor so I don't know for sure if all three need to be shorted.

Do you understand how the safety switches work ?
If any of the three is open.... the system(module) is activated.

Don't connect the module. Check the wire pairs first.
You need to confirm that each switch is shorted/closed.
Based on your meter lead resistance.... anywhere up to 10 ohms is probably ok.

How do the switches work ?
Possibly if the trans and deck are activated..... getting off the seat stalls the engine.
Turning off the trans and deck and doesn't make a difference if someone is on the seat.

 

Well YOU knew how many OHMs were supposed to be between the aforementioned contact points. Nobody else has chimed in with THAT key piece of information! Go to the head of the CLASS!

 

Checking the switch wires was the first check I made . The Blade switch and trans switch would kill the engine whether I was on seat or not. (I could start the engine without being on the seat after it came back from being rebuilt, (new rings, cylinder bore and hone, valves etc) I cannot remember whether it (the seat switch) did that BEFORE it went for the rebuild) When I checked the seat switch the other day, it was opening and closing with showing continuity (or not)but I don't remember what position (on or off the seat ) the mower was in on that check. I will check them all again, and determine the position that closes the seat switch circuit. Everything was working after the engine was rebuilt last year, but the starter had to draw a lot more current to kick the engine over, Never blew any fuses but something else may have been overworked in the wiring somewhere blowing out the module. That ability ( battery current draw affecting the module) doesn't appear to be a direct wiring clue., but maybe I just can't see it yet. If everything else fails, persevere! Thank you for your comments!

 

I've been out of town for a while and just now catching this, but based on what I'm reading I would say you most likely have a bad seat switch or related wiring or a bad module.

 

Hi Chuck! I may have already said that I checked all 3 switches, including the seat, and they all had no shorts, and would test fine with the on and off when they are supposed to (except the seat switch, I could always start the engine either on or OFF the seat as long as the other two switches were closed (deck and tranny. they were normally closed. The owners manual said nothing about having to be on the seat to start the engine, ONLY to be on the seat when engaging the transmission and or the deck. I have a new module which is NOT in the machine. It has checked out as having 3 ohms of resistance between some of the circuits where there is not supposed to be any, but I am still smart enough to be my OWN safety switch for now. I have enough mowers around here that if I burn out another switch I can get by, but I like this one for some tight spots my sunstar or HMR cannot get into lol I did not know the engine would run with the module removed, old dog, new trick!

 

Right, but looking at your diagram, not being on the seat with either of the other two switches opening will cause the engine to shut down. So I would say your problem is one of the three things mentioned. It cranks and runs until you engage one of the other switches, right? So the module is likely working properly as it reads the open and shuts down (transistor is switching) unless it's the part of the circuit on the green wire involving just the seat switch. That is possible. So I'm sticking with it being one of those 3. If you've eliminated one, then it's down to wiring or module according to your test. You mentioned the resistance tests, I'm not sure where that was taken. If the test was done at the module connections and both yellow to brown and also green to brown are zero or low resistance, then the wiring is probably fine and then you are left with a bad module. If the tests were taken up at the switches, I would say move to the module connections and do again to eliminate a wiring problem. If all that checks out, it seems like the module would be bad, the part switched by the green wire.

 

Hi Chuck, Just to confuse the issue I want to be clear that if I am on the seat or OFF the seat (with the old module) engaging the deck or transmission, will shut the engine down. My resistance tests were made on the bench with the two modules, old an new side by side with my ohm meter AND using the probe on the module connections not on the wires going to it. I was getting NO resistance reading on the new module where Pete told me It should be zero. but i WAS getting like 3 ohms of resistance on the OLD module, but a follow up from someone said that that was not a significant amount. If the 3 ohms WAS a significant amount this case would be case closed and I could just install the new module and hope for the best, but I would rather not fry the new one for a loss of 80 bucks, if you get my drift lol (from your reply it looks like the next thing I should do is test the wiring FROM the switches TO module for shorts or resistance levels unless I am reading you wrong?

 

Right, if you didn't check the switch operation at the module connectors, then do that. 3 ohms is pretty insignificant for this purpose. The interlock module thinks you are not on the seat. It allows you to start and run as long as the pedal and PTO aren't engaged. If you engage one, it shuts off the mower, correct? That means it thinks you aren't on the seat. The fact that it works properly otherwise means the brown wire is operational. The green wire is suspect, OR the module on the leg that the green wire activates.

 

I dont want to interrupt the conversation here, so take my thought as a side note & move on if its incorrect.

WML13 says sitting on the seat & engaging either of the two will kill the engine. He has checked the switches and he says they're good. The pro, Mr Cheese is convinced the switch is possibly bad. I do agree, but I am basic knowledge & I look at the basics.

My question here is, WML13, are you sure that when you sit on the seat it depresses the button on the safety switch. I've seen them move or get out of alignment....
or something blocks the seat & prevents it from going down enough to depress the switch fully, therefore not activating the switch.

Ensure that the button in/under the seat is being depressed/activated... all the way down.... enough to activate the switch.

 

Dixie, (and Chuck) I tested the Seat switch (and the other two) with OHM meter probes, not a visual on the switch itself, (was dealing with a house full of contractors and floor installers (after a leaking toilet in an upstairs bathroom started pushing its way down thru the rotting floor (the former owner was (6 letters starting with F) when whoever installed the toilet cut out the 2X10's that SHOULD have remained under the toilet base surrounding the Toilet flange) Credit to the flooring guy for making everything come out even!), (new sections of 2/10's New subfloor, and new tiles) (and oh yeah, lining up with a copper toilet flange that was almost an inch higher than the old floor surface) SO now that The lavatory of death is back in operation, I can focus on the Toro's switches! Thank you all for the help on this!