Need Help with troubleshooting ignition switch on Murray 12.5 HP

[MTD]

Hello,

I am looking for some assistance with determining whether the ignition switch on a Murray Lawn tractor (model # 40508x92G) is good or bad.

What I need to know specifically is what positions should give continuity and which ones shouldn't.

I have included the factory electrical diagram for my mower, and AFAIK ( I won't assume anything) it is correct for my mower. I double checked the wire colors on the harness and they do match what is shown on the attached diagram 100%

If someone sees that a simple continuity check for this particular switch/circuit would be inconclusive in knowing 100% whether the switch is ok or not, please point that out to me.

In case anyone is wondering, what happens is turning the key to start does absolutely nothing, just a small click - no engine turn over, nothing. Fuse is GOOD, The battery tests strong (12.75V), and, I think I have ruled out the solenoid. There is full voltage coming into the solenoid (RED lead), but I get no voltage on the ORG lead (when disconnected and measured as I turn key to START). Maybe the PTO safety switch but I want to rule out the ignition switch first.

Thanks,

Alan

 

[EngineMan]

I think you can rule out ignition switch because you are getting a click...!
You can check this by taking off the small lead on solenoid and seeing if you have battery volts on the lead when key is in start.
Give the ground lead a good clean and take off the solenoid and where it bolts to ground give that also a good clean and the big leads, and if that does'nt do the tick replace solenoid.
I don't think its a safety switch because you are getting a click, if one of the safety switch(s) was open you wouldn't get a click at solenoid.

Have a look at this post and you will see.......

http://www.lawnmowerforum.com/small...have-12-volts-but-still-starting-problem.html

 

[MTD]

I think you can rule out ignition switch because you are getting a click...!
You can check this by taking off the small lead on solenoid and seeing if you have battery volts on the lead when key is in start.
Give the ground lead a good clean and take off the solenoid and where it bolts to ground give that also a good clean and the big leads, and if that does'nt do the tick replace solenoid.
I don't think its a safety switch because you are getting a click, if one of the safety switch(s) was open you wouldn't get a click at solenoid.

I would have thought so too, but as I had said, when I did the voltage check on the small solenoid lead as you described I got 0 volts when the key was turned to START which would seem to point elsewhere since the voltage is not getting there.

I checked ground continuity from solenoid mounting bolts to several points of bare metal on the chassis and they all checked good. I will go now and check the ground lead on the switch wiring harness and see if tests good to the solenoid frame bolts.

Also wanted to add that when doing a continuity check with the switch in the OFF position I'm getting a very dodgy reading from Ground (pin 6) to Stator (Pin 4), which I think should be a clean low ohm reading for OFF? I'm getting anything from 24ohms to 3K to 5.6M (essentially open). Moving the key causes it to jump around indicating a poor contact. Perhaps the internal Ground connection in the switch is bad. Any thoughts?

 

[EngineMan]

Ground (pin 6) to Stator (Pin 4), is just for you're light's, have you got 12v at pin 2, if so check the safety switch(s)

 

[MTD]

Ok. I'm getting no continuity from the switch harness ground wire to the solenoid frame or to other bare metal chassis points. Unless I'm misreading the schematic it would appear to be a bad ground connection.

 

[EngineMan]

Would that be the Black wire...?

Find some wire, about 12in long, bear off both ends and fold back, take off small lead on solenoid hold one end on the small connecter that you took of the wire off from, now with ignition switch off, touch with other end the big lead that come's from the battery to the soleniod, engine should turn over.

 

[MTD]

The single black wire with O ring connector shown in the pic is the other end of the switch harness ground wire. It had apparently come loose - but from where is a bit of mystery at the moment. There is no clear obvious place of connection. Both of the solenoid frame bolts are tightly secured and there are no other loose bolts or bolt holes that I can see in the proper locale. There are only two frame screws (conical ended sheet metal type with no bolt) that are within reach of the ground wire. I suppose it does not matter where I reattach the ground provided it is well secured and stable. Any thoughts on where it likely was originally?

 

[EngineMan]

The single black wire go's to ground, if it fit's one of the bolt's that hold the solenoid on put it there.
Going by the wiring diagram it go's on solenoid ground as above....!

 

[MTD]

I secured the loose ground wire to the solenoid frame. Still will not start.

Also still No Voltage on small solenoid hot lead when measured while turning key to START.

Ground (pin 6) to Stator (Pin 4), is just for you're light's, have you got 12v at pin 2, if so check the safety switch(s)

I do have 12V at pin to, so on to safety switches. I wonder if the ground coming loose caused failure of one of the safety switches. Seems unlikely to have them both go out at same time.

Any suggestions on how to test the switches, assuming I can reasonably access them?

 

[EngineMan]

Set you're meter to Ohm's 1 connect one end to Orange lead that you have taken off solenoid, and the other to Pin 5 on the ignition switch, which is also Orange, you should have continuity, if you don't you have a bad wire between there going to all safety switch(s) or a safety switch that is open. so work you're way back from Orange lead at solenoid to Pin 5 ignition switch. checking each safety switch in turn.