308 wiring harness in a 312-8 - Can I?

[CCox 8]

I have a 312-8 (31-12K804) with wiring gremlins.  I have chased these for a few years and I finally reached a point where I have to do something.  I had eliminated the test lights several years.  What I have done is pulled the original wiring harness out to find the shorts.  I transplanted the wiring from a 308 since its much simpler.  I am down to the point of connecting the 308 plug with 3 pin plug (black/blue stripe, black/white stripe and black/green stripe).  I am thinking that this connects to the engine plug for the magneto but would like to confirm with someone more knowledgeable.  My engine is a Kohler M12S spec 471527 and it has a 5 pin plug (low oil shutdown).

 

Can I make insulated jumpers between these two plugs to use while I hunt the gremlins on the original harness?  If so, what gets jumped from the engine to the 308 harness that I am using?  Does anyone make replacement wiring harnesses for our tractors?

 

Thanks in advance.

Edited June 2, 2019 by CCox

[953 nut 51,488]

I agree that the 312-8 wiring with all the relays and test lights is mighty complicated compared to the 308-8 wiring. The plug to the engine on your 312-8 has only two wires you need to have connected. The two tan wires and an orange wire were for the low oil level sentry switch and relay, you don't have them on your "new" wiring harness. The wiring diagram I found for the 308 had an unregulated diode that provided power to the lights through a Dark Green wire that you won't need. You will need to connect a feed for your lights, the Light Green wire feeds the lights going from the light switch. You should run a new wire from your ignition switch "A" terminal (has a pink wire on it that feeds the hour meter) with a 10 Amp fuse to feed the light switch.

The white wire connects the Regulator/Rectifier to the "R" terminal of your ignition switch and is needed. The Dark Blue wire connects the Magneto to the safety switches and then to the "M" terminal of your ignition switch. These are the only wires you need to connect to the engine.

3 hours ago, CCox said:

Can I make insulated jumpers between these two plugs

Yes you can, I wouldn't bother with the old 312-8 harness, just replace it with the 308 one and have fun driving your 

 

[CCox 8]

I have made it through the summer with zero electrical headaches.  Had to strip my 312-8 to the frame due to a significant crack on the frame plate where the gearbox bolts on.  Repaired that, painted the frame, reassembled and fixed a number of other things in the process.  Now as the days grow shorter, I need to work on my headlights.

 

I have purchased wire in the basic colors and also picked up the original style non-insulated terminal ends to create my replacement harness including the plug that connects to the ignition switch.

 

What I haven't done is connect my headlights, hour meter, or amp meter.  I'd also like to think about building the low oil shutdown relays into the new harness.

 

Here is what I am trying to figure out:

1. Would the headlight circuit run from the ignition switch A (accessory) or should this be on the engine yellow wire?  And where should the switch and fuse be?

2. Would the amp meter circuit run from battery positive to a fuse, to the meter then to ignition switch B (battery) terminal?  

3. Would the hour meter run in the same circuit as the amp meter?

4. On the Kohler Oil Sentry switch, one lead is grounded, one lead (white) goes where and how does the relay fit into this scheme?

 

I plan to mock this up on the current (308) harness and then replicate it in new heavier wire.

 

Thanks in advance.  Its fun but sometimes a little overwhelming.  I'm hoping the new wiring will give me another 20 years free from headaches.

Edited September 21, 2019 by CCox

[953 nut 51,488]

54 minutes ago, CCox said:

1. Would the headlight circuit run from the ignition switch A (accessory) or should this be on the engine yellow wire?  And where should the switch and fuse be?

2. Would the amp Volt  meter circuit run from battery positive to a fuse, to the meter then to ignition switch B (battery) terminal?  

A 15 amp fuse will connect to the "A" (accessory) terminal of the ignition switch to the hour meter and volt meter as well as the headlight switch.

3. Would the hour meter run in the same circuit as the VOLT meter?

 

[CCox 8]

Thank you 953!  Its humbling to realize how little I know about circuitry.