Deere STX38 will not start with the key [Solved]

[rrrhre2s]

I have a couple of questions:

Does this engine have a magneto or 12 ignition coil system ?

Does the switch ground the Ignition in the off position ?

Sometimes the switches for the two systems can get mixed the one that grounds the ignition in the off position is for the magneto system.

The other one feeds 12 volts for the ignition coil in the on position...

Something wrong with the safeties may be causing the ignition to be shorted to ground on magneto type system.

Unhook the wire at the magneto and do an ohms check to ground with the battery disconnected, switch in the on position, everything in the normal position for starting and see if the wire is shorted.

First time I seen this was a tractor that had a Briggs engine on it but most of that brand used Koler at the time. The Koler used a 12 volt ignition system.

rrrhre2s

[aceatpool]

Thanks luffydog..............
The problem I'm having is getting it to crank with the key. It starts and runs fine if I can get to to crank. I don't know what else to check other than what I've already done if you have read the previous posts. I'm sure it is something simple (it most always is) but finding what that "something simple" is has alluded me thus far.

[aceatpool]

Thanks rrr but I'm not sure what you are saying. As far as I know it is a magneto system. I'm not sure I know what a 12 ignition coil system is. All the safeties work except for the one that I jumped. I don't think there are any shorts/problems in the wiring. I guess I'm going to have to buy another JD switch just to satisfy my mind that the "new" switch is good or bad............. Nothing else makes any sense to me. Have you read the other post on this problem?

[38racing]

At the switch the white wire pair should be on the M terminal so with connector off test that switch terminal for continuity to ground. Should have it in off and not have it in run. If in fact it is correct but it will run (ie has spark) in off position , then there is a discontinuity in the path from the coil. That path has a wire from coil to the brake switch where it hooks to a common connector and continues on to the key switch. (does not go through any switching at the brake switch). Given that the brake switch also has the crank circuit going through it and your crank function is also screwy maybe the wires are not attached correctly at the brake switch. Interesting also is that the path from the coil to the key switch is part of the circuit going back out to the pto and seat safeties which ground through different paths. I wonder if ,when you have it running in the off position, it would stay running even if you engaged the blades. That would be consistent with a break (open) in the kill circuit somewhere between the coil and the key switch. Appears to be all white wiring.

[Arkie]

Thanks luffydog..............
The problem I'm having is getting it to crank with the key. It starts and runs fine if I can get to to crank. I don't know what else to check other than what I've already done if you have read the previous posts. I'm sure it is something simple (it most always is) but finding what that "something simple" is has alluded me thus far.

You wrote this in your first initial post.

Unit will crank but not start.

Now you say later that it will start and run if you can it to crank.

This might give you a general idea of some of the starter solenoid wiring and safety switchs. (we can only surmise without a wiring diagram)

If it's a magneto system or 12v coil system you need to check for ignition spark, because most likely it won't have spark (if it cranks and won't start)
The keyswitch you have appears to be for a magneto system and the M (magneto) terminal applies a ground to kill the ignition)

If it won't crank with the key you need to take a voltmeter and check the two small terminals on the starter solenoid. (if its a isolated base type starter solenoid 12v will be applied from the keyswitch in the start position to one of the small terminals and the safety switches complete the circuit on the other terminal to ground. If you have 12v on both small terminals when key is turned to start a safety switch is open.
Does your starter solenoid have one small terminal wire or two.
AND
we need to know if the engine cranks and don't start or if it's not even cranking. Appears we have been told both???
AND
Do you have a voltmeter/Ohmmeter??

[rrrhre2s]

I think you have a Kohler CV12.5-1215 engine...

Magneto Ignition...

Is it Cranking and not starting or not cranking ?

rrrhre2s

[aceatpool]

Thanks to all who have responded with help/suggestions. This is becoming more confusing by the minute. Let me attempt to re-clarify the problem as briefly as I can.
The unit came to me with a “will crank but will not run properly” condition. The unit tried to run (cranking OK, spark OK, safeties OK, fuel supply OK) but acted like it was getting too much fuel. The motor shook violently (all mounting bolts were gone).I investigated and found the trouble. It was purely mechanical & had no bearing on the electric or wiring. The only wire I disconnected was the wire to the mower clutch since I had to pull that to get the motor off so I could chase the mounting bolts holes. The carb had dropped the throttle plate into the combustion chamber & eventually got stuck under the intake valve. I solved that problem successfully. I put everything back together without incident.
I then tried to crank/start the unit sitting on the seat, brake depressed and mower clutch switch “off” as one would do normally. NOTHING not even a click of the solenoid. It was DEAD……………the nightmare began since it cranked & tried to run BEFORE the motor repair??
I checked battery voltage. It was 12.31VDC. A little low so I charged the battery. Battery cables/connections seemed OK. Tried again………nothing. Jumped from battery to solenoid terminal, key “on” & the unit started, ran & idled just fine???? First blush, safeties not made for some reason. I checked them all to the best of my ability & they all seemed OK. Next check was wiring continuity. I’m not a pro at troubleshooting or reading schematics but better than average. I do have a service manual & a volt/ohm meter. After many checks and head scratching I determined the switch must be bad even though it was working when it came to me because I could jump from the hot to the solenoid in the wire harness & it would crank but not run (no power to the coil)!! I checked per the service manual and the switch checked bad. Ah HAAA, new switch needed!! I bought an aftermarket switch, installed it and still NOTHING!!! Now WHAT???? I checked the seat safety OK. I checked the mower clutch switch (per manual) OK. I checked the brake safety not sure as I was getting same readings across all terminals open or closed. I jumped the brake safety harness. I then tried to start it again. It would crank but not run????? As I turned the switch “off” while the motor was still turning due to inertia it caught & ran???? That’s strange????? An inspection of the 2 switches determined that the aftermarket switch & the John Deere switch had the ground in a different position. Deere switches aren’t lettered so I had no way of knowing if the rest of the terminals were the same. I don’t have those skills! I decided to buy a new John Deere switch from the dealer. Installed it and again………… NOTHING!!! I’m not a big fan of switching wires around as it can cause problems for the next guy that works on it. If it were mine I’d probably switch the wires on the harness. I’ve decided to buy another switch from the dealer just in case the 1st one was bad. It is rare but it does happen.. That is where I am at NOW!!! If that does not resolve the issue I have NO CLUE!!!
I’m sure many of you guys could easily find the problem if you had access to the unit. I know how difficult it is to diagnose problems over emails. I’ve done it and it ain’t fun!! I’ve had problems solved by this board several times before & I am eternally grateful for that but this one is a brain teaser for me!!!

[Deere2me]

Thanks to all who have responded with help/suggestions. This is becoming more confusing by the minute. Let me attempt to re-clarify the problem as briefly as I can.
The unit came to me with a “will crank but will not run properly” condition. The unit tried to run (cranking OK, spark OK, safeties OK, fuel supply OK) but acted like it was getting too much fuel. The motor shook violently (all mounting bolts were gone).I investigated and found the trouble. It was purely mechanical & had no bearing on the electric or wiring. The only wire I disconnected was the wire to the mower clutch since I had to pull that to get the motor off so I could chase the mounting bolts holes. The carb had dropped the throttle plate into the combustion chamber & eventually got stuck under the intake valve. I solved that problem successfully. I put everything back together without incident.
I then tried to crank/start the unit sitting on the seat, brake depressed and mower clutch switch “off” as one would do normally. NOTHING not even a click of the solenoid. It was DEAD……………the nightmare began since it cranked & tried to run BEFORE the motor repair??
I checked battery voltage. It was 12.31VDC. A little low so I charged the battery. Battery cables/connections seemed OK. Tried again………nothing. Jumped from battery to solenoid terminal, key “on” & the unit started, ran & idled just fine???? First blush, safeties not made for some reason. I checked them all to the best of my ability & they all seemed OK. Next check was wiring continuity. I’m not a pro at troubleshooting or reading schematics but better than average. I do have a service manual & a volt/ohm meter. After many checks and head scratching I determined the switch must be bad even though it was working when it came to me because I could jump from the hot to the solenoid in the wire harness & it would crank but not run (no power to the coil)!! I checked per the service manual and the switch checked bad. Ah HAAA, new switch needed!! I bought an aftermarket switch, installed it and still NOTHING!!! Now WHAT???? I checked the seat safety OK. I checked the mower clutch switch (per manual) OK. I checked the brake safety not sure as I was getting same readings across all terminals open or closed. I jumped the brake safety harness. I then tried to start it again. It would crank but not run????? As I turned the switch “off” while the motor was still turning due to inertia it caught & ran???? That’s strange????? An inspection of the 2 switches determined that the aftermarket switch & the John Deere switch had the ground in a different position. Deere switches aren’t lettered so I had no way of knowing if the rest of the terminals were the same. I don’t have those skills! I decided to buy a new John Deere switch from the dealer. Installed it and again………… NOTHING!!! I’m not a big fan of switching wires around as it can cause problems for the next guy that works on it. If it were mine I’d probably switch the wires on the harness. I’ve decided to buy another switch from the dealer just in case the 1st one was bad. It is rare but it does happen.. That is where I am at NOW!!! If that does not resolve the issue I have NO CLUE!!!
I’m sure many of you guys could easily find the problem if you had access to the unit. I know how difficult it is to diagnose problems over emails. I’ve done it and it ain’t fun!! I’ve had problems solved by this board several times before & I am eternally grateful for that but this one is a brain teaser for me!!!

In one of yer posts you said you had a wire diagram, but can't post it, OK, but just about EVERY wire diagram I've run across , including J.D., has an ign. switch INTERNAL CONNECTION diagram/chart/legend included somewhere on it!! A quick "stx38 wiring diagram" GOOGLE brought up several diagrams, all of which included the ign sw. legend.
Did you compare the original JD switch that was on the unit to the JD switch ya bought? When I say "compare", I mean wring it out with yer meter? Does yer meter have an audible diode/continuity checker? Sure makes life simpler .
I recently had a JD with same problem, was the brake switch, which was a dpdt switch. Most of the safeties are more than a simple on/off type. You might find the problem could be in the PTO switch, as the start circuit usually feeds thru it on most units.

[Arkie]

I see some stx38 wiring diagrams (several) and some have a 1 amp fuse and diode in the start (crank) circuit. look for the fuse and check the fuse and diode for continunity. Some diagrams show that the start circuit is from S1 to S2 on the keyswitch to apply 12v to the starter solenoid.

Find S1 wire on the ignition switch and check for 12v with key on. If no 12v check the 1 amp fuse and then the safeties, (seat switch and brake clutch switch. You have to have 12v on S1 on the keyswitch in the on position first then this 12v is applied to S2 during crank which is connected to the starter solenoid on most of the diagrams.

[aceatpool]

I haven't given up YET. I'm still trying to work through 38racing's suggestion "seems to be all white wiring" & Deere2me suggestions about the dpdt brake safety switch and the wiring paths. Would not it be quite uncommon for the ign switch & the brake safety to fail at the same time while just sitting in the shop? The unit starts/runs/drives/mows & everything works normally with the aftermarket switch but it only runs in the "off" position. That is what is so crazy about this whole ordeal!!!I didn't knowingly do ANYTHING to the wiring & now nothing seems RIGHT about the wiring. I haven't determined yet if the aftermarket & the JD switches are reverse images of each other. Seems like if they were the aftermarket switch would certainly not work in ANY switch position. Weather has not been favorable lately and the unit is outside covered with a tarp at the moment. No space in the covered area...........