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312-8 Won't start; dim seat switch light

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Hello everyone,

Sorry to make an account and post for help right away, but I plan on sticking around for a while. Anyway, I'm having a hard time getting my 312-8 tractor to start. It's got a Kohler Magnum 12 engine and the ID under the seat is 2112K806 (space) 37223. A few weeks ago it decided it didn't want to start; when the key was turned to the run position, the seat switch light was dim or flickering very faintly. I assumed the switch was dead, as it didn't have a distinct "click" when it was pressed any more and the tractor is approaching about 30 years of age.

I just got a replacement seat switch from Toro and installed it, but the tractor still refuses to start. The first few times, the seat switch appeared to be working correctly but the tractor insisted the clutch wasn't pushed in, according to the dash lights. I came back a few minutes later and the tractor still refuses to start, although now the seat switch light is behaving as it did before. If I leave the key in the run position and get off the seat, the light works correctly and lights up brightly and solidly, but sitting back down causes it to pulse and light dimly again. I've tried engaging and disengaging the PTO clutch, which the dash reports correctly, as well as the regular clutch, which also seems to respond correctly now.

I'm hoping you fine folks might be able to help me, as the tractor is going to get sold if I don't get it running and it's quite important to me. Any and all help is greatly appreciated, and I thank you in advance for your help!

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check the motor oil level

there are 3 safety switch's that will keep the tractors from starting if the key switch is good
PTO lever switch
clutch pedal depress switch
oil level switch
also check 25amp fuse


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Thanks for the advice, Brian!

This probably comes off as a stupid question, but where would I find the 25 amp fuse? My original manuals are long lost by the previous owner and the only fuse I see is one that's clipped to the battery tray; it looks like a regular automotive fuse and it looks good to me. I believe the oil level should be fine but I'm sure it needs to be changed very badly - where would I find the drain for the oil, and what viscosity should I replace it with?

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Here is a good detailed wiring diagram. Each circuit has it's own diagram.

Is the problem the starter won't engage and run to crank the motor over or
No ignition so motor won't run.

There are 2 pto switches.
One controls the starter along with the clutch pedal switch and the low oil relay.

The 2nd pto switch controls the ignition along with the seat switch.

There is a chance you have bad grounds. May be worth while to remove and clean them up.


Here is the 1989 operator manual

Kohler operator manual


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Thanks for the diagrams and advice, Garry!

I think you're probably right about the grounds being bad. I just got the tractor to start and it ran great - once it was running, the seat switch was working perfectly, killing the engine when I stood up with the PTO clutch engaged, but once I parked it again and attempted to start it, it went back to looking like the circuit is bad. I can see the wires coming from the seat switch and know the black one is the ground, but I can't find where it is grounded to the chassis as the cluster disappears under the instrument panel. I was wondering if anyone knows where the seat switch is grounded on this model or has an idea based on other models as I'm at a loss for where to look.

I also forgot to add - the ignition works fine; my issue is the tractor refusing to run the starter motor when I turn the key to the start position.

Edited by OneWithWaves

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use a jumper wire from the + battery terminal to the 1/4 blade terminal on the starter solenoid  to check if the solenoid is good you can also jump a cross the large terminals on the starter solenoid
this should make the starter motor run to check that


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Hi everyone,

Sorry for disappearing for a week but I haven't had the opportunity to put some more work into this tractor until today. It took me an embarrassingly long time to find the seat switch ground, which was bundled with many of the other grounds on a terminal connecting to the battery's ground. I took these grounds apart and cleaned up the connectors with some light sandpaper; the years of service had definitely done a number on some of them. I put the whole thing back together and got the starter to crank for one attempt, which got me excited (the tractor starts reliably, but only if it gets about three shots with the starter motor), but then the symptoms from the beginning of this thread cropped up again. Now, I'm not sure if maybe I missed another ground wire somewhere or if it could be a problem with the solenoid, as Brian's mentioned. It just seems strange that the dim seat switch light could be a symptom of a bad solenoid. Anyway, I found it on the tractor but it seems a little different than most of the solenoids I've seen (and I'll admit I haven't seen too many before). It looks like it only has two terminals and a ground, and from my understanding there are generally 3 or 4 terminals with a ground. I've included a picture of this solenoid - would I still test this one as Brian suggested or is there something different about this one?

Thanks for all your help this far!


PS When you look at the photo, notice the ground isn't actually grounded to the frame of the tractor, but a small ground wire connects it to the bundle of grounds I mentioned earlier in this post.

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