Help, difference between "internal" v.s. "ext

392hemi · Sep 13, 2018

Hello, I have a John Deere 318 garden tractor. The wiring diagrams from the shop manual gives 2 wiring diagrams. 1 with internal ground system and 1 with external ground system.
I'm a little familiar with 12v automotive systems, but am struggling to understand how my tractor is supposed to be correctly wired for starting and running properly??
Can anyone help explain (in simplistic) form how this works. Thank you

Steve@Advance · Sep 13, 2018

I'm not sure how that would refer to the entire system.

Look closely, it may refer to a specific component, like a starter solenoid, voltage regulator, etc. that may have an external ground terminal or is grounded internally through the chassis mount.

Just a guess...

jeffcat · Sep 13, 2018

Another guess would be how the ground is set up. I have seen machines grounded battery to frame and or battery to the engine. Old style JD mowers go to the engine. Newer stuff just gets screwed to the chassis.

Bob · Sep 13, 2018

On the earlier serial-numbered units, various circuits were grounded to separate pieces of the superstructure or frame, and, over time rust, corrosion, or loose bolts cold affect the electrical system.

On later units, grounds from all electrical components were connected inside the wiring harness to a common ground wire that bolted to the engine, making for just one connection with the potential to get loose, rusty, or corroded.

Battery is (of course) connected (-) ground, to the engine, as well.

If you are looking at the factory tech manual (TM1590), it's explained in the footnotes on Page 240-10-2.

<img src = "http://oi66.tinypic.com/2rzubme.jpg">

Wisconsin Cowman · Sep 13, 2018

There should be a serial number break for the wiring diagrams. If I remember right there is three different wiring harness used depending on serial number/ years.

392hemi · Sep 13, 2018

Thank you for your help. The Technical Manual I have is TM-1277. I missed the foot note, but I have read the bottom of the page that references the difference between S/N's. I don't understand the difference between the ( -475001 ) and ( 475001- ), other than it means higher and lower??
It's a long story, so I'll spare you-all. But I just had to replace the Onan engine with a different used Onan engine. I do have written down the new S/N

392hemi · Sep 13, 2018

Thank you for the thought. It's confusing for me as the "repair" process has been dragged out now for a few years. And I've had to replace several electrical components.

392hemi · Sep 13, 2018

Ok, Thank you

392hemi · Sep 13, 2018

Thank you, Yes, it does ground directly from batt. to bolt on top of engine block

392hemi · Sep 13, 2018

The Technical manual does show 2 different wiring diagrams. I get confused as I'm pretty sure the first diagram is correct, " External ground " but the second wiring diagram " Internal ground " actually shows all the components or parts that the tractor has installed. Whereas the 1st diagram isn't showing all the parts that are in the tractor.
If I go by the correct wiring colors, the 1st diagram would be correct and I think I'll stick with that. Thank you all for your help and advice. You folks are a fountain of knowledge!

Help, difference between "internal" v.s. "ext

392hemi

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