wheel horse 312H rescue

[terc 7]

Good morning, all

I am trying to rescue a 312 h. After a though cleaning I can get the engine running by jumping the solenoid, however the engine will not turn off with the ignition switch.   After replacing the ignition switch with a new 6 connector switch the engine will not stop by turning off the switch. I am unable to locate a wiring diagram for the ignition switch. I will say there some burnt & melted wires from the old switch. Also, the new switch does not have any markings as to what the terminals are. All of the safety switches are nonfunctional, which most are disconnected. I guess what I am looking for is a wiring diagram without all of those safety switches. Also how do I id the kill wire coming from the engine??  Thanks in advance

[Gasaholic 304]

Probably a Kohler Magnum 12 engine , which is magneto igniton, so you'd have 3 wires coming from under the flywheel - 2 white wires in a black wrapped harness are the AC output to regulator the third wire, I believe should be green or black  is the ignition module ground.  Wiring diagram can be found in the forums in the Manuals section https://www.wheelhorseforum.com/files/ 

 

You will want to be careful about unknown switches for wheel horse, you do not want to have any 12 volt power going to the magneto ground or you're going to need a new ignition module. So, you'll want key on and test for voltage before connecting any of those wires to anything connected to the engine - Unless you positively identify which wire is which. 12v to the magneto will smoke it. 

[953 nut 60,348]

Not all Wheerl Horses are wired alike, if you can provide the model number we can get you a proper wiring diagram. You should be able to find a model number on a sticker under the seat.

Be sure the switch you use is correct, 312s changed switch configurations a few times.

 

[terc 7]

Thanks for the quick replies 

Supporter Yes the engine is a Kohler Magnum 12 s engine here is a picture of the wiring coming from under the flywheel. Those two red wires are not connected to anything, I dont know what they need to be connected to. Also looks like the previous owner may have replaced the module.

953 nut sorry that I don’t have any model numbers the have been long gone. The replacement switch is the same configuration of the original switch with no marking on the blade terminals.

[Gasaholic 304]

Hmm I think you have a Command-  Your engine looks more like a Command series - I spy your engine model and spec tag just behind your throttle control cables in your last picture - a clear shot of that model tag (Or write out the Model Spec and Serial numbers here) we could get you more positive identification - a newer 312-8 (Look for your tractor's model serial tag and grab a picture of it - located under seat on seat pan, typically)  would be even more helpful  My memory's foggy but the purple wire in your harness may well be the ground (If it is indeed a command CH12S) , or it may be the carburetor's anti-afterfire solenoid (if it had/has one)  BUt your best way to be 100% sure which wires are which would be to remove the engine shroud front cover (Blower Housing) so you can see if the ground wire is actually hooked up to the magneto (COuld be the prior owner left it unhooked because they fried the first 1 or 2 modules after screwing up wiring elsewhere and sending 12V to the module!) If they left it unhooked for that reason, you found why the engine wont shut off, but then you have to fix all the wiring screwups they did that caused it in the first place, which can be a troublesome slog for the un-initiated... 

[953 nut 60,348]

2 hours ago, terc said:

The replacement switch is the same configuration of the original switch. The ignition switch turns off the ignition by grounding the magneto so if the switch is not grounded it will never turn off the engine.

There are dozens of ignition switches that will plug into the five terminal plug but only the correct switch will give proper operation. 

All 300 and 400 models that were equipped with Kohler Magnum engines from 1987 to 1991 used the 103991-ignition switch and from 1992 to 1997 they all used the 116338-ignition switch. These two switches are not interchangeable.

Use a multi-meter to see what switch your 312 had (the old one) and compare it tt the new one to see if you guessed right w2hen you bought it.

[kpinnc 14,712]

59 minutes ago, Gasaholic said:

Hmm I think you have a Command-  Your engine looks more like a Command series -

 

Definitely a Magnum 12. Even if no sticker the oil pan is identical to a K-series as it should be. 

 

Command engines are all aluminum on the block construction. This is a cast iron block. 

 

 

[terc 7]

I will report back with pictures of the spec plate and with the blower housing removed

 

[gwest_ca-(File Mod) 11,522]

The Kohler wiring shows a white wire to kill the ignition and a violet wire from the regulator B+ to charge the battery.

This is not shown on the Wheel Horse wiring diagrams.

Wish I had included it when coloring the original diagrams.

[clueless 3,263]

3 hours ago, gwest_ca said:

The Kohler wiring shows a white wire to kill the ignition and a violet wire from the regulator B+ to charge the battery.

This is not shown on the Wheel Horse wiring diagrams.

Wish I had included it when coloring the original diagrams.

 looks like you have a 1990-1992 312-H with the magnum, during those years they had two different ignition switches, 103991 and 111215, they are not compatible, do you have the old original switch? You definitely need to use the correct switch, it doesn't take much to screw up everything. If you go to the manual section here and find the manual for the 1990, the 1991 and the 1992 model you will find the wiring diagram for all of them, then you just need to figure out which year you have, trust me the mysterious smoke just loves folks who assume.

[terc 7]

gwest_ca-(File Mod)  I can verify that the purple wire does go to the  engine stator from the connector plug. Also the white wire from the engine coil to the connector plug changes to a dark blue wire that continues to the ignition switch

Clueless i have the  what is believed to be the original 6 connector switch, which I have replaced with another 6 connector switch. I will continue to look at those manuals you listed. I am really finding this wiring from a previous owner challenging  to say   Thanks again for everyone's help in this endeavor  

[terc 7]

Gasaholic  Here is a better picture of the engine model tag to get a positive identification of the engine and possibility identification of the tractor, since the tractor model tag is long gone

[Gasaholic 304]

OK so engine should be about 1990 model year so likely a 3112KE01 or thereabouts for model number. 

 

[953 nut 60,348]

Kohlere spec # 471527 on M12S engines was used from 1987 to 1997. @Gasaholic is shooting from the hip here.

You need to use a multimeter to check the old switch against the diagram I gave you in post number 6 and compare it to the new switch to be sure you have the correct switch. Not turning off the engine is likely to be a matter of the ignition switch not being grounded.

On 7/30/2025 at 10:48 AM, terc said:

there some burnt & melted wires from the old switch.

The poor condition of your connector could be the reason you need to jump the solenoid or the fuse holder from thr battery side of the solenod to the ignition switch could be corroded or the fuse mau hav e blown.

Take this one step at a time, confirm that you are using the correct ignition switch and that the switch body is grounded when installed. 

Once that has been done use a small jumper wire from the battery + to the small terminal of the solenoid that has a small blue wire on it. This should cause the solenoid to operate.

Let us know what you find.

[Gasaholic 304]

15 hours ago, 953 nut said:

Kohlere spec # 471527 on M12S engines was used from 1987 to 1997. @Gasaholic is shooting from the hip here.

 

Sort of - I came up with 1990 model year based on engine serial number.... since we have yet to have a whole overall shot of the tractor itself with details, and they can't seem to find a model number tag for the tractor, Shooting from the hip is about all any of us can really do - engine serial number, assuming it is original of course, can get "sort of close" to model year, and from that can generally infer what tractor model and year is "likely" to be.... m

[953 nut 60,348]

34 minutes ago, Gasaholic said:

"sort of close"

That is also "sort of close" to the year Wheel Horsae changed ignition switches which could result in the wrong switch being used.

[Gasaholic 304]

Yep. Without the tractor model/serial tag all we can do is guess - narrowing it down to being "unlikely" to be earlier than 1990 or later than 1991 *assuming* the engine is original can help somewhat at least to be aware of which wiring diagram to use, and what to look out for.  - So, if it is *likely* a 1990 , possibly 1991 model year 312-H, and *unlikely* to be a 1992 (but not impossible) -  one can at least eliminate switches/wiring from earlier or later as being *low probability* - nothing's for sure (Even if I had the model/serial tag on the tractor, given how messed up the existing wiring is, there's no sure bets.)  

 

However, if it was me, I'd grab the closet matching wiring diagram and assume a specific model year (and thus parts catalog) and *make* the tractor switches and wiring match up (Though that'd take a bit of expertise in wiring and testing circuits, etc. plus a whole lot of wire- multiple spools of color coded wire, or at least colored tape to tag out wire ends, so it isn't a whole lot of help to the original poster, I'd guess.) 

 

Like I'd posted initially - have to be careful of different switches - lot of switches can plug into the harness, but any BUT what was meant to be there can cost you a ton more of headaches, money and time.. 

[terc 7]

953 nut  I will need to verify as to which small terminal you are referring to as there are no wires connected to mine, also can you verify the black box mounted next to the solenoid. As you can see I am also replacing the fuse block as the old one had some issues.   

Edited August 1 by terc
adding picture

[gwest_ca-(File Mod) 11,522]

The black box is likely the relay for the low oil switch.

Starting in 1992 they added a second seat relay for the 312.

[953 nut 60,348]

I agree with @gwest_ca that the small black box is your low oil relay.  1992 and later 312s would have several relays as shown below so it seems likel yours is a 1991 or earlier. There is a gtood reason your solenois isn't working, it is missing two wires.

In your case the light blue wire goes to the ignition switch S terminal.

[clueless 3,263]

My man said he is trying to rescue a 312-H, the 312-H was produced in 1990 to 1992, so if he knows it's a 312-H there is are just 3 years to chose from. All came with the Kohler M12 and according to all three wiring diagrams the are wired the same except the ignition switch changed at some point and the added seat switch. As Richard said his is a 1990/91. He says he has the original ignition switch, a photo of the back of it would help in stopping some of the guessing and assuming here. The 1990/91 have the same wiring diagram, over the years for me having the correct wiring diagrams goes a long way in rewiring a cobbled up, (lack of a better term)  wiring mess.

Edited August 2 by clueless

[953 nut 60,348]

Chris @clueless,         good detective work there.         You told me you didn't like wiring but here you are up to your elbows in it.       

The lack of a seat relay tells us it is not 1992 and since the wiring diagram for the 1990 and 1991 are the same and the "H" was only made during those three years the attached pages of the Demystification Guide should be very helpful to @terc.

 

[clueless 3,263]

12 hours ago, 953 nut said:

Chris @clueless,         good detective work there.         You told me you didn't like wiring but here you are up to your elbows in it.       

The lack of a seat relay tells us it is not 1992 and since the wiring diagram for the 1990 and 1991 are the same and the "H" was only made during those three years the attached pages of the Demystification Guide should be very helpful to @terc.

 

Richard, I still don't like wiring, but I've learned over the years to do as much research   as I can find on a tractor before I ask you guys for help. As I said it cuts down on the guessing, BS and assuming posts, I'm already confused, don't need more . Also I'm a text book case ADHD person, your going to lose me quick with to much information .

Enjoy your Sunday.

[953 nut 60,348]

[terc 7]

On 7/30/2025 at 10:48 AM, terc said:

 

Thank you to the membership for your support on the 312 h rescue. I’m glad to report that all tractor system is working as they should, on my first tractor ride today. Your support means a lot, again thank you for your valuable assistance. I will be using this tractor as a support tractor to get a feel on how it’s going to run and work out any possible issues. Now to move on to the mower deck repair.