Wiring diagram for 24 volt starter

chas036

Member
I have a JD 720 diesel with an electric start that came without any wiring or starter or switches. I just bought a 40mt 24 volt starter which fits perfectly in the starter bracket that I want to use to start it. Also I bought two 12 volt 800 CA batteries which fit in the battery box, and I bought a 24 volt low turn alternator to charge the batteries.

What I need is help with how to wire it all up from scratch. If someone could send me a basic wiring diagram on how I would connect the ignition switch and battery to the starter, and how I would wire up the alternator back to the batteries, and where the amp meter connects in, and what size wire I would need, I would greatly appreciate it.

I know this is not original and I am not looking to restore it to original. I just want something that is reliable and will start the diesel and charge the batteries. I don't have lights or the fuel gage, so that is not an issue.
 
If you are going to connect it up as a straight 24 Volt system with the negative side connected to the chassis you would simply wire it up like you would a 12 Volt system, only difference being you will connect the two 12 Volt batteries in SERIES, making 24 Volts.

Be aware that with the full 24 Volts above chassis ground, there'll be some pretty nasty sparks, arcs, or melting, if anything ever shorts or you bridge a tool, a (finger) ring, or a watchband between the 24 Volts and the chassis.

It would have been easy to keep the original (+)12 (-)12 system, and that's what I would have done, but if this is your choice, it's easy to do.

If you want an Ammeter, connect it into the charging wire from the alternator.

Be SURE you understand the connections at the starter and solenoid and BE CAREFUL, don't cause shorts as previously mentioned and wear eye and face protection when working around the batteries. What is this, a 40 Amp alternator... use 10 gauge or even 12 gauge wire for the alternator wiring, it's a good idea to include a fusible link or fuse of reasonable size (based on alternator output rating) to protect the alternator wiring from short circuits.

If the connections at the starter appear different or you are unsure, post a photo of that area.

<img src = "http://oi63.tinypic.com/szzwno.jpg">
 
Thank you very much for the diagram. If I were to do it your way with a 12 volt charging system , I would assume that I would have to use a 12/24 parallel switch. Can you show a diagram for that?

If the 24 volt ground system is more dangerous, then I will take the 24 volt alternator back and get a 12 volt alternator and go with the 12 - 24 parallel switch if you can show me how to wire it and recommend a switch to get.
 
Here is a pic of my starter
mvphoto19661.jpg
 
I think you will be fine... I had an 830 years ago with a 24 volt system like you are proposing... no real issues, but, as I said, it sure makes for a big spark when you do accidentally do something that shorts the 24 Volts to ground.

Series-parallel switch lets you use a 12 Volt alternator and lights/accessories, but in return, adds complexity and a LOT of wiring and connections.

You say you don't need accessories/lights and have the 24 Volt components, give 'er a go!
 
Bob,,,do I need to ground the 24 volt system to the frame of the tractor to get the alternator to work, or will the alternator work just as you have it in your diagram?

I like your set up with the starter motor grounded directly to the battery and isolated from the frame? I would prefer to keep the whole system isolated from the frame if possible.
 
My diagram shows the starter AND the negative side of the battery grounded to the frame/chassis.

Unless you have an "isolated" ground alternator, the alternator is already grounded to the chassis thorough it's "frame", and keeping the 24 Volt system isolated from the chassis isn't possible.

Got a photo of the back of the alternator?

This sort of stuff makes posting and replying to posts about this sort of thing risky, because there are different versions of 24 Volt starters and alternators, some with all the internals isolated from the frames/housings and the wrong answer can let the $$$$ smoke out of an alternator or wiring harness almost instantly!
 
Bob,,,,,

My alternator is a normal type that is grounded to the tractor through the mounting bracket, so I am going to ground the whole 24 volt 2 battery source to the frame with the standard JD ground cable that is in the battery box.

What size wire should I use coming from the positive post of the battery to the solenoid on the starter as depicted in your diagram? Also size wire from the ground on the starter to the chassis?
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top