1959 JD 730 Diesel starter wiring

[Sonofa730owner]

New to the site and appreciative of any guidance I can get. My dad has a 1959 JD 730 Diesel, electric start, 24V which is wired positive ground. He had a starter problem and pulled it for repair. He marked all the wires (color coated) and the starter posts with the same colors so he would know were each wire goes when reinstalling. Did I mention he is 90 years old? Unfortunately the repaired starter and new solenoid was cleaned and painted, removing his markings. The large gage wires from the batteries are obvious. There are also three small gage wires. One has a ring connector that can only go on the power post on the solenoid. This leaves two small wires with small connectors, which is my question. Are they both ignition wires that attach to the same solenoid post? Thanks all in advance.

 

[Tx Jim]

Welcome to this forum
Technically JD 730 24 volt diesel starter/generator electrical system is not positive or negative ground as it has ""no ground connection to tractor frame"". Yes the 12 volt electrical accessories have a positive & negative ground wires see parts item #18. Take notice of color of wires in parts schematic & their location on starter & solenoid. , ,

 

[Sonofa730owner]

Welcome to this forum
Technically JD 730 24 volt diesel starter/generator electrical system is not positive or negative ground as it has ""no ground connection to tractor frame"". Yes the 12 volt electrical accessories have a positive & negative ground wires see parts item #18. Take notice of color of wires in parts schematic & their location on starter & solenoid. , , View attachment 161561

Thanks for your quick responds and schematic. Unfortunately the solenoid has been replaced with a new one and doesn't have the same looking posts. (see image) The large ring (Blue) looks like it attaches to the same as the power from the battery. Looks like the brown and black wires come from the ignition switch (10)? That when switched on turns on a light. Would both of those wires connect to the single small post on the new solenoid?

 

[Tx Jim]

JD dealership where I was formerly employed only had a very few 720/730's with diesel powered engines so I have very limited personal experience with them. Can you determine original colors of each wiring harness wires that were designed to attach to starter & it's solenoid? I think that type 24 volt solenoid was only utilized of JD tractors with 2cylinder diesel powered engines. I suggest acquiring a JD 720/730 D electrical tech manual.

 

[Sonofa730owner]

JD dealership where I was formerly employed only had a very few 720/730's with diesel powered engines so I have very limited personal experience with them. Can you determine original colors of each wiring harness wires that were designed to attach to starter & it's solenoid? I think that type 24 volt solenoid was only utilized of JD tractors with 2cylinder diesel powered engines. I suggest acquiring a JD 720/730 D electrical tech manual.

The solenoid that was replaced definitely looks different than the one that was bad. Are you saying the new solenoid may not be made for 24V?
I do plan on attempting to strip the green paint from the wires.

 

[Tx Jim]

No I'm not stating your current starter solenoid isn't for 24 volts. 24 volt solenoids I remember seeing have 24V stamped on mounting bracket

 

[used red MN]

Hello son, welcome to YT! I have no hands on experience with those tractors or their 24v start system. The things that are adding to the difficulty of assisting you is your photo is not the best. Do all 3 small wires shown go back into a harness as 3 individual wires? Also in Jim’s diagram where the number 3 points down at the starter it is not real clear what that all is representing. Maybe Jim could provide the description associated with 3.

 

[Sonofa730owner]

Hello son, welcome to YT! I have no hands on experience with those tractors or their 24v start system. The things that are adding to the difficulty of assisting you is your photo is not the best. Do all 3 small wires shown go back into a harness as 3 individual wires? Also in Jim’s diagram where the number 3 points down at the starter it is not real clear what that all is representing. Maybe Jim could provide the description associated with 3.View attachment 161645

I will be going to my dads today and will attempt to strip the green paint front the wires to get a better sense of wire color code. I believe they all come from a common sleeve or wire. Thanks for your interest.

 

[m16ty]

I've got a 730 diesel with electric start. I can take a look at it tomorrow and try to get you a pic of how it's wired.

 

[Sonofa730owner]

I've got a 730 diesel with electric start. I can take a look at it tomorrow and try to get you a pic of how it's wired.

Thanks for your reply. I was able to contact the guy that rebuilt the starter and he was able to answer my question. The two posts in question on the original solenoid simply moved straight up onto the face of the new solenoid. So the brown wire when to ground and black to ignition.

 

[Sonofa730owner]

Thanks to all. Consider this one closed.

 

[buickanddeere]

Actually the JD 24V system Is both positive and negative ground together at the same time.

 

[Tx Jim]

Actually the JD 24V system Is both positive and negative ground together at the same time.

Actually JD 24 volt 12 volt accessory circuits have positive & negative grounds. I was taught at John Deere service school that I attended in Dallas Tx at JD branch location many yrs ago that the starter, generator & voltage regulator have no ground connection to tractor frame. ALL afore mentioned parts were attached to a piece of plywood then attached in 24 volt fashion to two 12 volt batteries. Starter was engaged & generator was powered via a v-belt and electric motor with DC volt gauge attached to prove 24 volt starting/generating circuit requires no frame ground!!!!

 

[buickanddeere]

Actually JD 24 volt 12 volt accessory circuits have positive & negative grounds. I was taught at John Deere service school that I attended in Dallas Tx at JD branch location many yrs ago that the starter, generator & voltage regulator have no ground connection to tractor frame. ALL afore mentioned parts were attached to a piece of plywood then attached in 24 volt fashion to two 12 volt batteries. Starter was engaged & generator was powered via a v-belt and electric motor with DC volt gauge attached to prove 24 volt starting/generating circuit requires no frame ground!!!!

Performed a similar demonstration at the NY Expo nearly 20 years ago . Some audience members were considering it was witchcraft. A few looked under the plywood expecting to observe jumper wires .

 

[TheBartman47]

A 24v system is similar to house wiring... Home 240v with a center tap as neutral to get two legs of 120v. Think of the two 12v batteries like the transformer on the powerline pole with a center tap, batteries in series.

 

[Tx Jim]

I agree 240 volt AC electrical system resembles 24 volt DC electrical system but the center tap/neutral on 240 volt AC system isn't both + & - polarity like the 24 volt accessory circuits

 

[m16ty]

I agree 240 volt AC electrical system resembles 24 volt DC electrical system but the center tap/neutral on 240 volt AC system isn't both + & - polarity like the 24 volt accessory circuits

Well it actually is, it changes polarity 60 times a second in the US, 50 in the UK.

The JD system really doesn’t change polarity on ground. The JD setup is really 3 separate separate circuits and all 3 work independent of each other. You have the 24v circuit for starting and charging, you have 1/2 of the accessory load on another circuit that is positive ground, then you have the other half of the accessories that are on another circuit that is negative ground. The frame ground doesn’t change from positive to negative, it’s both at the same time.

It’s a pretty ingenious way to pull 12v off a 24v DC system and still keep everything somewhat in balance. There are other more modern ways to do it but they are quite a bit more complicated.

 

[TheBartman47]

And remember, "ground" is just a reference point. Technically, there is no polarity to ground because all voltages are measured with reference to "ground", which is by definition 0 volts (thus, no polarity at all). There are 3 basic ground types (other ground variations include Analog ground or Digital ground, protected ground, etc.) but all are at 0 voltage. On that tractor, the starter circuit is -12v to +12v for a total of 24v, some accessories will be at -12v, and others at +12v.

 

[Tx Jim]

IMHO comparing JD 24 volt electrical system & 240 AC electrical system just adds confusion to the average tractor repair person that's not a very knowledgeable AC electrician.