My Tractor Forum banner
  • We have a new contest celebrating your backyard. Sponsored by Walmart, its your chance to win a $400 gift just in time for the 4th of July! HERE Contest Ends on the 30th.

Not open for further replies.
1 - 1 of 1 Posts

2,189 Posts
Discussion Starter · #1 ·
Hey Guys,

This thread is a follow up to the thread i made on upgrading my 20 amp magneto style stator to a 40amp alternator.

I did some basic research online and could not get a definite answer on whether the 40 amp alternator is a direct replacement(minus running a wire to the start for charging). It's not a direct replacement. I believe John Deere sells a kit that comes with everything for around $400 or maybe more.

I studied wiring diagrams from my 455 service manual and found out enough information to try it out and see if i could make it work factory.

And I did!

A little Background info

The factory 20 Amp charging system:
Uses the stator style alternator, which produces ac voltage and sends it through two wires harness to a Voltage regular/Rectifier. It is then converted to DC voltage and charges the battery.

The 40 Amp charging system
Uses an automotive style alternator, with a built in Voltage regulator/Rectifier. It has a large power wire to send Current to charge the battery. It uses the same style 2 wire harness, but uses one wire for a 12V "reference excitement" wire, and the other goes to the idiot light in the dash.

This first picture shows the factory charging system


New 40 amp alternator

40 amp alternator mounted using factory belt and brackets/bolts
the top bolt goes in from the opposite side then the factory alternator.

Here is when the Problems persists.
The factory charging system idiot lights works like this:

The indicator light is always grounded, when the charging system is not charging, the voltage regulator sends 12V+ to the light to turn the light on.
Simple enough....

The 40 amp charging system idiot light works like this:

The indicator light always has 12V+ going to it, when the charging system is not charging, a post on the alternator grounds out the wire coming from the idiot light, causing it to light up.

The way the idiot light works between the two charging systems is completely opposite. Since i believe the whole instrument cluster works on a common ground with the 20 amp charging system. It would be quite difficult to have 12V going to the light all the time, and getting a ground wire from the light to the terminal on the alternator.

This is where the expensive John Deere wiring harness comes in.

So i engineered this solution:

Use a simple SPST automotive relay

12V Constant(red wire)= 30
12V Switched(yellow wire)=86
Ground to alternator Terminal(Black wire hooked into one of the AC leads on the Factory Harness, Must use a Continuity tester to determine correct wire)=85
Wire to idiot light in dash(Brown wire)=87

Quite a simple design, The relay is open when the charging system is working, and when it is not charging the alternator ground out the relay cause it to close and send 12V+ to the indicator light.
This allowed me to have a working idiot light.

This picture shows the VR and wiring harness

Harness unhooked

Here is the Relay installed in the way listed above.
The Horizontal Terminal of the "T" connector on the back of the alternator gets 12V+ switched from the Yellow wire on the VR Harness.

As stated above, the Black wire from the ground Relay #85 Gets hooked to the Vertical Terminal of the "T" connector on the back of the alternator. There fore when the charging system is not working it ground the relay and sends 12V to the light in the dash.

You will need a continuity tester to verify which AC wire goes to what terminal on the alternator using the factory harness(color codes are the same)

This picture shows the relay mounted and all wired in, Keep in mind i did NOT cut one wire, i used quick splice taps. If need, i could plug the VR back in and go back to the 20 Amp stator

Of course Bella is checking in to make sure i'm wiring it right..

When i turn the key on showing the idiot light working

I made the power wire at work using #8 gauge wire

Crimped and soldered


The install only took a half hour.

The alternator i purchased on Ebay for 77$

Relay and that was free from work but would only be about 5$

I fired up the tractor and idiot light went out right away, and the battery terminals showed 14.4V i turned on all my lights and accessories and battery light stayed off Woohoo!

I'm really happy i did the install and was the "Guinea Pig" as i seen alot of members inquired about upgraded and never got a definite answer on how to do it. so here it is.

I would encourage anyone to do the upgrade if using a Cab or power hungry accessories.

Any questions comments are welcome. Id be glad to Help anyone out.

This should go work on all diesels, 430,455,x495,x595 and gas ones equipped with the alternator.

If i can identify what the Large plastic connector at the VR is, and buy it with new pins, I will be able to wire up a unit with the relay that is plug and play, just unhook the Harness from the VR and plug it into the new unit. and install the red power wire to the starter and be good to go. Then it would be "plug and play" if any member is interested in doing the upgrade i may be able to assemble that to eliminate the guess work. i will be able to provide a Rear Plug and play 40 amp upgrade:trink40:

I included a video here at the end Try to Verbally explain the install and a start up showing the light working and all the accessories on.


Moderators, if this is sticky worthy feel free to do it:thThumbsU

1 - 1 of 1 Posts
Not open for further replies.